Internal Compiler Error

I now have this error in Unity 4.6.6 Error is below:

Internal compiler error. See the console log for more information. output was: Unhandled Exception: System.Reflection.ReflectionTypeLoadException: The classes in the module cannot be loaded.

at (wrapper managed-to-native) System.Reflection.Assembly:GetTypes (bool)

at System.Reflection.Assembly.GetTypes () [0x00000] in :0

at Mono.CSharp.RootNamespace.ComputeNamespaces (System.Reflection.Assembly assembly, System.Type extensionType) [0x00000] in :0

at Mono.CSharp.RootNamespace.ComputeNamespace (Mono.CSharp.CompilerContext ctx, System.Type extensionType) [0x00000] in :0

at Mono.CSharp.GlobalRootNamespace.ComputeNamespaces (Mono.CSharp.CompilerContext ctx) [0x00000] in :0

at Mono.CSharp.Driver.LoadReferences () [0x00000] in :0

at Mono.CSharp.Driver.Compile () [0x00000] in :0

at Mono.CSharp.Driver.Main (System.String[] args) [0x00000] in :0