public class ClientMustResubmitException
This exception exists to work around a bug in IE cause by hotfix Q832894 which occasionally causes the browser to fail to send data filled into a form when the form is submitted. The RPCManager logic automatically detects this condition and throws this exception.
In your RPC processing logic you should catch this exception and simply return. The RPCManager will have automatically sent a directive to the client-side RPCManager to resubmit the request.