Why is Assembly.GetCustomAttributes suddenly throwing TypeLoadException on build machine with Silverlight 4?

A short while back i had to display the current version of our Silverlight app. After some googling the following code gave me the desired result:

var fileVersionAttributes = typeof(MyClass).Assembly.
    GetCustomAttributes(typeof(AssemblyFileVersionAttribute), false) as AssemblyFileVersionAttribute[];
var version = fileVersionAttributes[0].Version;

This worked a treat in our .NET 3.5 Silverlight 3 environment. However, we recently upgraded to .NET 4 and Silverlight 4. We just finished getting our build machine working and found that the unit test for this code was throwing the following exception:

Exception Message: 

System.TypeLoadException: Error 0x80131522.  Debugging resource strings are unavailable. See http://go.microsoft.com/fwlink/?linkid=106663&Version=3.0.50106.0&File=mscorrc.dll&Key=0x80131522 
   at System.ModuleHandle.ResolveType(ModuleHandle module, Int32 typeToken, RuntimeTypeHandle* typeInstArgs, Int32 typeInstCount, RuntimeTypeHandle* methodInstArgs, Int32 methodInstCount)
   at System.ModuleHandle.ResolveTypeHandle(Int32 typeToken, RuntimeTypeHandle[] typeInstantiationContext, RuntimeTypeHandle[] methodInstantiationContext)
   at System.Reflection.Module.ResolveType(Int32 metadataToken, Type[] genericTypeArguments, Type[] genericMethodArguments)
   at System.Reflection.CustomAttribute.FilterCustomAttributeRecord(CustomAttributeRecord caRecord, MetadataImport scope, Assembly& lastAptcaOkAssembly, Module decoratedModule, MetadataToken decoratedToken, RuntimeType attributeFilterType, Boolean mustBeInheritable, Object[] attributes, IList derivedAttributes, RuntimeType& attributeType, RuntimeMethodHandle& ctor, Boolean& ctorHasParameters, Boolean& isVarArg)
   at System.Reflection.CustomAttribute.GetCustomAttributes(Module decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount, RuntimeType attributeFilterType, Boolean mustBeInheritable, IList derivedAttributes, Boolean isDecoratedTargetSecurityTransparent)
   at System.Reflection.CustomAttribute.GetCustomAttributes(Module decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount, RuntimeType attributeFilterType, Boolean isDecoratedTargetSecurityTransparent)
   at System.Reflection.CustomAttribute.GetCustomAttributes(Assembly assembly, Type caType)
   at System.Reflection.Assembly.GetCustomAttributes(Type attributeType, Boolean inherit)
   at MyCode.VersionTest()

I have never seen this exception before and the link in it points nowhere. It is only throwing on the build machine and not on my development box, so i'm going through a process of trial and error to see any differences between the two.

Any idea why this might be happening??

Cheers, Andrej.

Usually you would see TypeLoadException when a Silverlight assembly has been linked to desktop libraries and one its types accesses a system type that is not supported on Silverlight.

I can't really explain why it broke under Silverlight 4, but my guess it's something inside your silverlight library. Can you execute the same code on one of system types and see if it crashes?

typeof(string).Assembly.
    GetCustomAttributes(typeof(AssemblyFileVersionAttribute), false) as AssemblyFileVersionAttribute[];

If the above doesn't crash, start commenting out bits of MyClass to see which part of it causes TypeLoadException.