In developing my GWT application today, I encountered this error:
Have you forgotten to annotate your event handler with @Presenter or @EventHandler?
This one was a struggle to track down. In fact, the actual problem did not seem related to the error message at all. The problem was I was using a Java SDK class in my GWT client code that was not approved. In my case, I was trying to use java.util.Calendar. Once I removed the usage of that class, I was back on track.