Unable to start program C:\...\****.dll VB.net application Visual Studio 2015

Question

I have been working on a VB.net web application for some time now, and I accidentally switched the "Application Type" setting from a Class Library to a Windows Form Application. I tried to build, this failed, but when I switched back, the program would no longer execute, displaying the error:

Unable to start program 'C:\\Users\\User\\...\\bin\\Project.dll'
'C:\\Users\\User\\...\\bin\\Project.dll' is not a valid Win32 application.

Prior to this the application would build fine. Furthermore, in the properties page for the project, the "Web" section displays the error:

An error occurred trying to load the page.
Value does not fall within the expected range.

The build output offers no clues as to the unexpected behavior, it builds fine, it just won't run. The code is also fully functional.

I have tried restarting multiple times, deleting the /bin directory and allowing it to rebuild from scratch (then restoring the old contents when this failed), setting the startup project, changing the target CPU and debug/release mode. I have tried both ReSharper build, and Visual Studio build. I also tried making a build configuration that targeted 'C:\\Users\\User...\\bin\\Project.vshost.exe', but this would execute then close immediately. I have no option to set a "Startup Object" in the application page of the project settings, but this has never been an issue. I have never needed to target an EXE to run my application before. If I try other application types, it states "Sub Main was not found in project".

I cannot recreate the project due to it's size so would love it if anyone could offer some insight, next time I will be mindful not to play around with the IDE settings.

======= UPDATED =======

So I fixed the "not running issue" by changing the WebProjectProperties to:

<UseIIS>True</UseIIS>
<UseCustomServer>False</UseCustomServer>
<servers defaultServer="">

But now when I run the program, the following error is displayed:

Could not load file or assembly 'Microsoft.VisualStudio.QualityTools.UnitTestFramework (2)' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

System.IO.FileLoadException: Could not load file or assembly 'Microsoft.VisualStudio.QualityTools.UnitTestFramework (2)' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

Stack trace and details:

---

=== Pre-bind state information ===
LOG: DisplayName = Microsoft.VisualStudio.QualityTools.UnitTestFramework (2)
 (Partial)
WRN: Partial binding information was supplied for an assembly:
WRN: Assembly Name: Microsoft.VisualStudio.QualityTools.UnitTestFramework (2) | Domain ID: 2
WRN: A partial bind occurs when only part of the assembly display name is provided.
WRN: This might result in the binder loading an incorrect assembly.
WRN: It is recommended to provide a fully specified textual identity for the assembly,
WRN: that consists of the simple name, version, culture, and public key token.
WRN: See whitepaper http://go.microsoft.com/fwlink/?LinkId=109270 for more information and common solutions to this issue.
LOG: Appbase = file:///C:/Users/User/Source/Repos/Findem/IfitConsulting/
LOG: Initial PrivatePath = C:\Users\User\Source\Repos\Findem\IfitConsulting\bin
Calling assembly : (Unknown).
===
LOG: This bind starts in default load context.
LOG: Using application configuration file: C:\Users\User\Source\Repos\Findem\IfitConsulting\web.config
LOG: Using host configuration file: C:\Users\User\Documents\IISExpress\config\aspnet.config
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config.
LOG: Policy not being applied to reference at this time (private, custom, partial, or location-based assembly bind).
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework/v4.0.30319/Temporary ASP.NET Files/vs/0ef61219/b7128029/Microsoft.VisualStudio.QualityTools.UnitTestFramework (2).DLL.
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework/v4.0.30319/Temporary ASP.NET Files/vs/0ef61219/b7128029/Microsoft.VisualStudio.QualityTools.UnitTestFramework (2)/Microsoft.VisualStudio.QualityTools.UnitTestFramework (2).DLL.
LOG: Attempting download of new URL file:///C:/Users/User/Source/Repos/Findem/IfitConsulting/bin/Microsoft.VisualStudio.QualityTools.UnitTestFramework (2).DLL.
WRN: Comparing the assembly name resulted in the mismatch: NAME
ERR: Failed to complete setup of assembly (hr = 0x80131040). Probing terminated.

Stack trace

[FileLoadException: Could not load file or assembly 'Microsoft.VisualStudio.QualityTools.UnitTestFramework (2)' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)]
   System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +0
   System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +36
   System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, RuntimeAssembly reqAssembly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks) +152
   System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean forIntrospection) +77
   System.Reflection.RuntimeAssembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +21
   System.Reflection.Assembly.Load(String assemblyString) +28
   System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +38

[ConfigurationErrorsException: Could not load file or assembly 'Microsoft.VisualStudio.QualityTools.UnitTestFramework (2)' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)]
   System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +738
   System.Web.Configuration.CompilationSection.LoadAllAssembliesFromAppDomainBinDirectory() +217
   System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai) +130
   System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig) +170
   System.Web.Compilation.BuildManager.GetPreStartInitMethodsFromReferencedAssemblies() +92
   System.Web.Compilation.BuildManager.CallPreStartInitMethods(String preStartInitListPath, Boolean& isRefAssemblyLoaded) +290
   System.Web.Compilation.BuildManager.ExecutePreAppStart() +157
   System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException) +531

[HttpException (0x80004005): Could not load file or assembly 'Microsoft.VisualStudio.QualityTools.UnitTestFramework (2)' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +9947380
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +101
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +261

Answer 1

Ok so finally figured out how to fix it, hopefully this can help some other poor soul who ends up in the same situation!

The first step is to edit your project.vbproj file and change:

        <WebProjectProperties>
      <UseIIS>False</UseIIS>
      <UseCustomServer>True</UseCustomServer>
      <servers defaultServer="SelfHostServer">
        ...
      </servers>
    </WebProjectProperties>

To

        <WebProjectProperties>
      <UseIIS>True</UseIIS>
      <UseCustomServer>False</UseCustomServer>
      <servers defaultServer="">
        ...
      </servers>
    </WebProjectProperties>

Then, you want to go to your /bin directory and delete the following files (Project is your projects name):

Project.dll
Project.dll.CodeAnalysisLog.xml
Project.dll.config
Project.dll.CodeAnalysisLog
Project.pdb
Project.xml

And re-build and it all works fine!