I had the same problem in the past days. You can check in the ePO Interface.
Go to Email and Web Gateway where your registered appliances are. (I think Menu -> Gateway Protection -> Email and Web Gateway - I have only the german language for ePO )
At the end of the table you have more information. If you click here you should see the information about your appliance. If this is not shown, you see an error.
The problem by me was that i must corrected the user and password in ePO and WebGateway.
well...we could see the information.