Xamarin iOS could not AOT an assembly during build

Question

When building a Xamarin iOS application that I am in the process of migrating to the Unified Xamarin API, I am seeing a build error during the AOT phase of compilation. Error I am seeing is "Could not AOT the assembly" followed by the assembly name. I am building in Debug mode for a device (although I'm currently only building with support for the ARMv7 architecture).

The assembly that is failing to AOT compile is a binding DLL which I have written for a native 3rd party iOS library (which is proprietary, so unfortunately I cannot share it). The binding project DLL is included in a library, which is nuget packaged and installed in my Xamarin iOS application.

I have searched for this error and found a bunch of Xamarin forum posts and bugzilla entries and have tried most of the steps suggested including:

• Tried link all assemblies and link SDK assemblies only
• Tried removing simulator architectures from the native fat binary to reduce size, binary is now 5.3MB (based on this Xamarin forum post https://forums.xamarin.com/discussion/457/error-could-not-aot-the-assembly-servicestack-text-monotouch-dll )
• LLVM is disabled, but enabling and building results in the same error
• Incremental builds are already disabled
• Building in Xamarin Studio on Mac, same result

I've run a build with "-v -v -v -v" as additional mtouch arguments as suggested in several forum posts and attached the build log. I've also attached the system info from Visual Studio and Xamarin Studio on the Mac.

Verbose Build Log

8>------ Rebuild All started: Project: MyCompany.Apps.MyApp, Configuration: Debug iPhone ------
8>  Generated session id: 9004d64cf52132c032e74d7755ff80f4
8>  Generated build app name: MyCompanyMyApp
8>  Connecting to Mac server 172.22.11.38...
8>C:\Program Files (x86)\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(1135,3): warning : This file is set to build for a version older than the deployment target. Functionality may be limited.
8>C:\Program Files (x86)\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(1135,3): warning : This file is set to build for a version older than the deployment target. Functionality may be limited.
8>C:\Program Files (x86)\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(1135,3): warning : Tint Color before iOS 6.0
8>C:\Program Files (x86)\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(1135,3): warning : This file is set to build for a version older than the deployment target. Functionality may be limited.
8>C:\Program Files (x86)\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(1135,3): warning : This file is set to build for a version older than the deployment target. Functionality may be limited.
8>C:\Program Files (x86)\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(1135,3): warning : This file is set to build for a version older than the deployment target. Functionality may be limited.
8>C:\Development\TFS\Repos\My App\MyCompany.Apps.MyApp\BusinessLayer\MbProgressHud.cs(228,15,228,22): warning CS0108: 'MBProgressHUD.Dispose()' hides inherited member 'NSObject.Dispose()'. Use the new keyword if hiding was intended.
8>C:\Development\TFS\Repos\My App\MyCompany.Apps.MyApp\CameraScanning\CameraScanningScreen.cs(25,13,25,33): warning CS4014: Because this call is not awaited, execution of the current method continues before the call is completed. Consider applying the 'await' operator to the result of the call.
8>C:\Development\TFS\Repos\My App\MyCompany.Apps.MyApp\Conductors\UnscannedPositionConductor.cs(349,30,349,32): warning CS0168: The variable 'ex' is declared but never used
8>C:\Development\TFS\Repos\My App\MyCompany.Apps.MyApp\CameraScanning\CameraScanningScreen.cs(19,26,19,32): warning CS0169: The field 'CameraScanningScreen.cancel' is never used
8>  MyCompany.Apps.MyApp -> C:\Development\TFS\Repos\My App\MyCompany.Apps.MyApp\bin\iPhone\Debug\MyApp.exe
8>  Detected signing identity:
8>    Code Signing Key: "iPhone Developer: Daniel Wright (Developer ID)" (Code Signing Thumbprint)
8>    Provisioning Profile: "Unified MyApp Dev" (Provisioning Profile GUID)
8>    Bundle Id: com.mycompany.MyApp
8>    App Id: TEAMID.com.mycompany.MyApp
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/MyApp.exe
8>  Code: 685280(70%) Info: 9305(0%) Ex Info: 216891(22%) Unwind Info: 22042(2%) Class Info: 8701(0%) PLT: 1504(0%) GOT Info: 26867(2%) Offsets: 7561(0%) GOT: 15588
8>  Compiled: 1101/1101 (100%), No GOT slots: 0 (0%), Direct calls: 78 (9%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/MyApp.exe.armv7.s'.
8>  Linking symbol: '_mono_aot_module_MyApp_info'.
8>  JIT time: 178 ms, Generation time: 188 ms, Assembly+Link time: 2 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/MyCompany.Mobile.Scanner.dll
8>  Code: 19632(67%) Info: 206(0%) Ex Info: 6057(20%) Unwind Info: 1425(4%) Class Info: 256(0%) PLT: 54(0%) GOT Info: 1188(4%) Offsets: 447(1%) GOT: 616
8>  Compiled: 47/47 (100%), No GOT slots: 0 (0%), Direct calls: 6 (37%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/MyCompany.Mobile.Scanner.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_MyCompany_Mobile_Scanner_info'.
8>  JIT time: 7 ms, Generation time: 7 ms, Assembly+Link time: 0 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/MyCompany.MyApp.Logic.dll
8>  Code: 39688(66%) Info: 529(0%) Ex Info: 13263(22%) Unwind Info: 2187(3%) Class Info: 252(0%) PLT: 126(0%) GOT Info: 2766(4%) Offsets: 659(1%) GOT: 1240
8>  Compiled: 75/75 (100%), No GOT slots: 0 (0%), Direct calls: 16 (48%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/MyCompany.MyApp.Logic.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_MyCompany_MyApp_Logic_info'.
8>  JIT time: 14 ms, Generation time: 12 ms, Assembly+Link time: 0 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/SimpleInjector.dll
8>  Code: 1940724(68%) Info: 28134(0%) Ex Info: 611304(21%) Unwind Info: 55960(1%) Class Info: 8683(0%) PLT: 5839(0%) GOT Info: 156474(5%) Offsets: 24193(0%) GOT: 50748
8>  Compiled: 3768/3768 (100%), No GOT slots: 0 (0%), Direct calls: 714 (20%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/SimpleInjector.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_SimpleInjector_info'.
8>  JIT time: 455 ms, Generation time: 496 ms, Assembly+Link time: 11 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/mscorlib.dll
8>  Code: 2082300(63%) Info: 41502(1%) Ex Info: 785618(23%) Unwind Info: 137926(4%) Class Info: 25683(0%) PLT: 7807(0%) GOT Info: 179354(5%) Offsets: 39518(1%) GOT: 45356
8>  Compiled: 9033/9034 (99%), No GOT slots: 6159 (68%), Direct calls: 4126 (27%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/mscorlib.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_mscorlib_info'.
8>  JIT time: 965 ms, Generation time: 1545 ms, Assembly+Link time: 9 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/LineaProSdk.dll
8>  Code: 560344(73%) Info: 5775(0%) Ex Info: 173294(22%) Unwind Info: 8808(1%) Class Info: 8867(1%) PLT: 498(0%) GOT Info: 3425(0%) Offsets: 4777(0%) GOT: 5520
8>  Compiled: 810/810 (100%), No GOT slots: 0 (0%), Direct calls: 361 (37%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/LineaProSdk.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_LineaProSdk_info'.
8>  JIT time: 100 ms, Generation time: 114 ms, Assembly+Link time: 1 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/MyCompany.FeatureManagement.dll
8>  Code: 72972(66%) Info: 691(0%) Ex Info: 25265(23%) Unwind Info: 3321(3%) Class Info: 82(0%) PLT: 315(0%) GOT Info: 6593(6%) Offsets: 826(0%) GOT: 2092
8>  Compiled: 133/133 (100%), No GOT slots: 0 (0%), Direct calls: 19 (271%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/MyCompany.FeatureManagement.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_MyCompany_FeatureManagement_info'.
8>  JIT time: 21 ms, Generation time: 23 ms, Assembly+Link time: 0 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/MyCompany.MvvmMediator.dll
8>  Code: 19120(68%) Info: 155(0%) Ex Info: 6344(22%) Unwind Info: 1080(3%) Class Info: 77(0%) PLT: 51(0%) GOT Info: 1027(3%) Offsets: 298(1%) GOT: 480
8>  Compiled: 39/39 (100%), No GOT slots: 0 (0%), Direct calls: 12 (109%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/MyCompany.MvvmMediator.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_MyCompany_MvvmMediator_info'.
8>  JIT time: 5 ms, Generation time: 5 ms, Assembly+Link time: 0 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/MyCompany.Infrastructure.CRMApi.RestSharp.dll
8>  Code: 408928(70%) Info: 4642(0%) Ex Info: 129632(22%) Unwind Info: 10518(1%) Class Info: 1032(0%) PLT: 1036(0%) GOT Info: 24321(4%) Offsets: 3809(0%) GOT: 8200
8>  Compiled: 656/656 (100%), No GOT slots: 0 (0%), Direct calls: 166 (164%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/MyCompany.Infrastructure.CRMApi.RestSharp.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_MyCompany_Infrastructure_CRMApi_RestSharp_info'.
8>  JIT time: 102 ms, Generation time: 110 ms, Assembly+Link time: 2 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/MyCompany.Apns.Models.dll
8>  Code: 14376(73%) Info: 243(1%) Ex Info: 3745(19%) Unwind Info: 233(1%) Class Info: 217(1%) PLT: 3(0%) GOT Info: 329(1%) Offsets: 442(2%) GOT: 392
8>  Compiled: 81/81 (100%), No GOT slots: 0 (0%), Direct calls: 0 (100%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/MyCompany.Apns.Models.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_MyCompany_Apns_Models_info'.
8>  JIT time: 2 ms, Generation time: 4 ms, Assembly+Link time: 0 ms.
8>  WARNING: The runtime version supported by this application is unavailable.
8>  Using default runtime: v4.0.30319
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/RestSharp.MonoTouch.dll
8>  Code: 927864(69%) Info: 12723(0%) Ex Info: 302043(22%) Unwind Info: 27821(2%) Class Info: 4606(0%) PLT: 2160(0%) GOT Info: 44891(3%) Offsets: 11159(0%) GOT: 20856
8>  Compiled: 1756/1756 (100%), No GOT slots: 0 (0%), Direct calls: 137 (10%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/RestSharp.MonoTouch.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_RestSharp_MonoTouch_info'.
8>  JIT time: 215 ms, Generation time: 233 ms, Assembly+Link time: 3 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/Newtonsoft.Json.dll
8>  Code: 2482700(71%) Info: 30603(0%) Ex Info: 772302(22%) Unwind Info: 68998(1%) Class Info: 10671(0%) PLT: 4816(0%) GOT Info: 99573(2%) Offsets: 25548(0%) GOT: 44084
8>  Compiled: 4386/4386 (100%), No GOT slots: 0 (0%), Direct calls: 490 (9%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Newtonsoft.Json.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_Newtonsoft_Json_info'.
8>  JIT time: 532 ms, Generation time: 631 ms, Assembly+Link time: 9 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/System.dll
8>  Code: 825072(63%) Info: 16854(1%) Ex Info: 301613(23%) Unwind Info: 62678(4%) Class Info: 14664(1%) PLT: 3402(0%) GOT Info: 67408(5%) Offsets: 14019(1%) GOT: 20392
8>  Compiled: 3232/3232 (100%), No GOT slots: 2095 (64%), Direct calls: 886 (23%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/System.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_System_info'.
8>  JIT time: 388 ms, Generation time: 480 ms, Assembly+Link time: 6 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/SQLite.Net.Platform.XamarinIOS.Unified.dll
8>  Code: 46872(71%) Info: 511(0%) Ex Info: 13688(20%) Unwind Info: 2338(3%) Class Info: 289(0%) PLT: 132(0%) GOT Info: 1047(1%) Offsets: 806(1%) GOT: 1160
8>  Compiled: 127/127 (100%), No GOT slots: 0 (0%), Direct calls: 46 (46%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/SQLite.Net.Platform.XamarinIOS.Unified.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_SQLite_Net_Platform_XamarinIOS_Unified_info'.
8>  JIT time: 8 ms, Generation time: 12 ms, Assembly+Link time: 0 ms.
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/MyCompany.Mobile.Scanner.Ingenico.dll
8>  Code: 6656(64%) Info: 60(0%) Ex Info: 2172(21%) Unwind Info: 489(4%) Class Info: 234(2%) PLT: 22(0%) GOT Info: 543(5%) Offsets: 179(1%) GOT: 244
8>  Compiled: 17/17 (100%), No GOT slots: 0 (0%), Direct calls: 0 (0%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/MyCompany.Mobile.Scanner.Ingenico.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_MyCompany_Mobile_Scanner_Ingenico_info'.
8>  JIT time: 2 ms, Generation time: 2 ms, Assembly+Link time: 0 ms.
8>  AOT Compilation exited with code 134, command:
8>  MONO_PATH=/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build /Library/Frameworks/Xamarin.iOS.framework/Versions/9.8.1.4/bin/arm-darwin-mono-sgen --debug -O=gsharedvt  --aot=mtriple=armv7-ios,data-outfile=/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/MyCompany.IngenicoBinding.armv7.aotdata,static,asmonly,direct-icalls,full,soft-debug,dwarfdebug,no-direct-calls,outfile=/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/MyCompany.IngenicoBinding.dll.armv7.s "/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/MyCompany.IngenicoBinding.dll"
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/MyCompany.IngenicoBinding.dll
8>  Structure field of type SByte[] can't be marshalled as LPArray
8>  Mono Ahead of Time compiler - compiling assembly /Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/System.Xml.dll
8>  Code: 2006348(66%) Info: 49971(1%) Ex Info: 690337(22%) Unwind Info: 109834(3%) Class Info: 35208(1%) PLT: 5371(0%) GOT Info: 85523(2%) Offsets: 32316(1%) GOT: 36536
8>  Compiled: 7444/7444 (100%), No GOT slots: 4655 (62%), Direct calls: 734 (7%)
8>  Output file: '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/System.Xml.dll.armv7.s'.
8>  Linking symbol: '_mono_aot_module_System_Xml_info'.
8>  JIT time: 1004 ms, Generation time: 2190 ms, Assembly+Link time: 17 ms.
8>C:\Program Files (x86)\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(681,3): error : Could not AOT the assembly '/Users/user/Library/Caches/Xamarin/mtbs/builds/MyCompanyMyApp/9004d64cf52132c032e74d7755ff80f4/obj/iPhone/Debug/mtouch-cache/Build/MyCompany.IngenicoBinding.dll'
8>    at Xamarin.Bundler.AOTTask.Build () <0x111e89920 + 0x003be> in <filename unknown>:0 
8>    at Xamarin.Bundler.BuildTask.Execute () <0x111e89310 + 0x00010> in <filename unknown>:0 
8>    at Xamarin.Bundler.Target+<Compile>c__AnonStorey0.<>m__0 (Xamarin.Bundler.BuildTask v) <0x111e89030 + 0x00028> in <filename unknown>:0 
8>    at System.Threading.Tasks.Parallel+<ForEachWorker>c__AnonStorey6`2[TSource,TLocal].<>m__0 (Int32 i) <0x111e88ba0 + 0x00062> in <filename unknown>:0 
8>    at System.Threading.Tasks.Parallel+<ForWorker>c__AnonStorey3`1[TLocal].<>m__1 () <0x111e873f0 + 0x003d2> in <filename unknown>:0 
========== Rebuild All: 4 succeeded, 1 failed, 3 skipped ==========

Visual Studio Information

Microsoft Visual Studio Professional 2015
Version 14.0.25123.00 Update 2
Microsoft .NET Framework
Version 4.6.01038

Installed Version: Professional

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Common Azure Tools   1.7
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JetBrains ReSharper Ultimate 2015.2   Build 103.0.20150818.200216
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Xamarin   4.1.1.3 (34a92cd)
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Xamarin.Android   6.1.1.1 (7db2aac)
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Xamarin.iOS   9.8.1.4 (3cf8aae)
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Xamarin Studio Information

=== Xamarin Studio Community ===

Version 6.0.1 (build 9)
Installation UUID: ff72e804-2e29-4006-bfd0-7b3f4ea0aa24
Runtime:
    Mono 4.4.1 (mono-4.4.0-branch-c7sr0/4747417) (64-bit)
    GTK+ 2.24.23 (Raleigh theme)

    Package version: 404010000

=== Xamarin.Profiler ===

Not Installed

=== Xamarin.Android ===

Not Installed

=== Xamarin Android Player ===

Not Installed

=== Apple Developer Tools ===

Xcode 7.3.1 (10188.1)
Build 7D1014

=== Xamarin.Mac ===

Not Installed

=== Xamarin.iOS ===

Version: 9.8.1.4 (Xamarin Studio Community)
Hash: 3cf8aae
Branch: c7sr0
Build date: 2016-06-20 16:09:58-0400

=== Build Information ===

Release ID: 600010009
Git revision: e879ce52093257c5c386ad7e390dfaa937fa7f90
Build date: 2016-06-24 11:53:43-04
Xamarin addins: a9252e6df4851fbbed1f9c6228e7b6dd1b475ac5
Build lane: monodevelop-lion-cycle7-sr0

=== Operating System ===

Mac OS X 10.11.3
Darwin Users-Mac-4.local 15.3.0 Darwin Kernel Version 15.3.0
    Thu Dec 10 18:40:58 PST 2015
    root:xnu-3248.30.4~1/RELEASE_X86_64 x86_64

Answer 1

The build log says this:

Structure field of type SByte[] can't be marshalled as LPArray

The assembly in question has a structure with an SByte[] field and no [MarshalAs] attribute (which means it will be marshaled as an LPArray, which is the default).

That scenario isn't supported by the AOT compiler, so AOT compilation fails.

This must be fixed by the library vendor.