In Microsoft Dynamics CRM 2011, when you attempt to execute a plug-in, you receive the following error:
System.TypeLoadException: Could not load type 'System.Runtime.CompilerServices.ExtensionAttribute' from assemby 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'
System.TypeLoadException: Could not load type 'System.Runtime.CompilerServices.ExtensionAttribute' from assemby 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'