Simple but crucial item to check - have you ensured that the COM+ credentials are not locked out and/or the pw is entered correctly?  I say this only because I've seen this happen before, e.g., the account's password was modified and nobody told the LANDesk admin.

Really the only answer is that the Com+ objects have to run as a user that can enumerate the groups in a domain.

I have often seen the change to a username not work until after a reboot even though I stopped and started the objects.  You probably already rebooted though.

It looks like you are doing things right and if those Com+ objects are correct, the Domain\User and password are correct and working, and a reboot didn't fix it, then you have done nothing wrong at all.  It is probably something like a poorly registered .NET Framework or a problem with the Core Server's domain membership.

Again, you are doing it right, it should be working.

Looks like you are doing everything correct. I have to ask <grin>, have you changed the credentials on both COM+ objects? Also just to be sure it is not a account issue (some weird GPO restriction), change the credentials to your username and password, just for S&Gs.