Cannot bind to the target method

My game works in iOS, Android, Windows Desktop, but on Windows Mobile I get the following error:

 ArgumentException: Cannot bind to the target method because its signature or security transparency is not compatible with that of the delegate type. 
 at System.Reflection.RuntimeMethodInfo.CreateDelegateInternal(Type delegateType, Object firstArgument, DelegateBindingFlags bindingFlags, StackCrawlMark& stackMark) 
 at System.Reflection.RuntimeMethodInfo.CreateDelegate(Type delegateType, Object target) at UnityEngine.Events.InvokableCall..ctor(Object target, MethodInfo theFunction) 
 at UnityEngine.Events.PersistentCall.GetRuntimeCall(UnityEventBase theEvent) 
 at UnityEngine.Events.PersistentCallGroup.Initialize(InvokableCallList invokableList, UnityEventBase unityEventBase) 
 at UnityEngine.Events.UnityEvent.Invoke() at UnityEngine.UI.Button.Press() at UnityEngine.UI.Button.OnPointerClick(PointerEventData eventData) 
 at UnityEngine.EventSystems.ExecuteEvents.Execute(IPointerClickHandler handler, BaseEventData eventData) 
 ...

I cannot replicate it in the Unity Editor. It only appears to happen when running from a Windows Mobile device.

Any ideas what could cause this?