Vista - Problem joining AD domain

My Vista Ultimate machine has been working fine as part of an AD domain. However, suddenly it dropped out of the domain and into WORKGROUP mode. I can add it manually but after the first reboot it drops out again.

Thanks.

I was able to resolve the issue described in this post and wanted to document it for others.

PROBLEM:
Vista Ultimate machine suddenly falls out of the AD domain membership. Computer can be manually added to the domain but upon restart, it drops out again.

CAUSE:
Failed (incomplete) installation of the Altiris agent, AClient.exe. The network support group had released a silent push install to all computer clients via the Altiris Deployment Server.

SOLUTION:
Force remove Altiris agent by navigating in a command window to the installation folder, in this case c:\program files\altiris\aclient\ and issuing the command aclient /remove /silent. Client was subsequently reinstalled by network support group.

Hope this helps.
Thanks.