You've got a great GWT web-client application but you can't figure out why all your custom, server-side exceptions are rolling into your client app as anything but your custom exception. Yes, GWT supports custom exceptions as valid 'failure' responses back to your GWT client, but when they get to your handler all you see is IvocationTargetException: see server log." If you've done some research you may end up with: "Service method com.my.private.company.project.rpc.service.Classname.processLogin(java.lang.String) threw an unexpected exception: Invalid username / password." Dangit Scotty!