Could not load type 'System.Runtime.CompilerServices.ExtensionAttribute' from assembly 'mscorlib

Question

When starting up my web site for the first time, I\'m getting this error

Could not load type \'System.Runtime.CompilerServices.ExtensionAttribute\' from assemb

Answer 1

I just ran into this annoying problem today. We use SmartAssembly to pack/obfuscate our .NET assemblies, but suddenly the final product wasn't working on our test systems. I didn't even think I had .NET 4.5, but apparently something installed it about a month ago.

I uninstalled 4.5 and reinstalled 4.0, and now everything is working again. Not too impressed with having blown an afternoon on this.