We have not implemented this type of error message into our WAP terminal. So I think that this text "Gateway received an invalid response from the upstream gateway" comes from a web server used in the backend system. It can go like this: A web server responses with an error message in HTML format to the WAP Gateway. In the WAP Gateway it is translated to be in WML format and then the end user gets a wml deck displaying this text. What does the error message mean, that I really don't know.