You'd need to pick through the value types, email messages looking for that attribute CurrentGroup as it looks like you don't have one of those at whatever point it is being used on your system. Pay particular attention to where you might have typed something in rather than using the value type browser to add an attribute.
Like Dave said, it seems like there is a Value in some other location that doesn't match exactly to what Service Desk is looking for. I've had this happen before in other cases where I used something like "User" when it should have been "_User". Probably just a typo somewhere.