Build error with System.Web switching a C# project over from AnyCPU to x64

Question

I have a Visual Studio (2013) C# project that builds fine on AnyCPU is failing to build when I change the platform target to x64 . This is on .NET 2. The error I get is

An attempt was made to load an assembly with an incorrect format: C:\\Windows\\Microsoft.NET\\Framework\\v2.0.50727\\System.Web.dll.

I'm struggling to find what I should do here. I have tried re-adding Sustem.Web and resources I have read indicate that this reference should work for either platform (I presume it is itself AnyCPU ). I feel like I am missing something very obvious here...

Answer 1

It turns out it was caused by an AfterBuild event in the .csproj file that was invoking SGEN. Disabling "Generate serialization assembly" and removing this AfterBuild event resolved it.