ExecutionEngineException : JIT/AOT error when adding to delegate

Using Unity 4.6.1 My code is crashing with an ExecutionEngineException when I am adding a handler to a delegate event. The delegate's signature is public delegate void OnDelegate (string channel, string message); Its pretty simple with no generics. The delegate and the class in question are located inside a dll, if that has anything to do with it. My exception is : >ExecutionEngineException: Attempting to JIT compile method '(wrapper managed-to-native) System.Threading.Interlocked:CompareExchange (MyDll.OnDelegate&,MyDll.OnDelegate,MyDll.OnDelegate)' while running with --aot-only. Please advise.