In your PQL, you are working with [UID], which is retrieving the current User’s ID. But if I understand you right, you want to get the current User Group’s ID, which would be [GID].
I guess that’s the only problem. 🙂
PS: You can test any PQL by typing it into the bottom-left navigation search field (F11) after a “=”, such as “=[UID]”. That way, you can always see which value your PQL returns in a certain situation. If you open a case where the trigger should be fired, and you put in your (corrected) PQL, you should see a pop-up showing “1”.