Error encountered while using Forefront TMG software

Hi Experts,
I was trying to join a Forefront TMG server to an existing enterprise array. I then tried starting the service but then I got this error message (please see screenshot below). I wondered why I couldn’t join the server to the array. I checked the configurations and seemed fine. Anyway, any advice on what to do next?

ForeFront TMG Error
The operation failed.
Error: 0x0040431
Forefront TMG services failed to start after a array join or an array disjoin. Check alerts, fix the configuration, and attempt to restart the services.
