Web service doesn't return the FIRST out parameter

I am having a Silverlight 2.0 beta 2 app to make web service calls to the server side and gets data back from client side when they finishes.

Each webservice method contains a number of parameters. The first parameter is always an OUT parameter errorMessage, and the second parameter is also an OUT parameter errorCode.

In the WebService_Method_CallCompleted event handler on client side, it gives me the following error message on e.errorMessage:

'WebService_Method_CallCompletedEventArgs' does not contain a definition for 'errorMessage' and no extension method 'errorMessage' accepting a first argument of type WebService_Method_CallCompletedEventArgs' could be found (are you missing a using directive or an assembly reference?)

I'm pretty sure that the problem only occurs on the FIRST parameter (no matter what it is), as I put a dummy out paramet ...