Hi, I am also having an issue adding a domain to Desktop Central, even though I specify correct credential it gives me an error, "Validation failed."
I HAVE ADDED A DOMAIN BEFOR ON ADMANAGER WITH NO ISSUES.
error log:

[Tue Feb 26 09:29:58 2008] [notice] Parent: Created child process 3020
[Tue Feb 26 09:29:58 2008] [notice] Child 3020: Child process is running
[Tue Feb 26 09:29:58 2008] [notice] Child 3020: Acquired the start mutex.
[Tue Feb 26 09:29:58 2008] [notice] Child 3020: Starting 10 worker threads.
[Tue Feb 26 11:28:35 2008] [notice] Parent: Created child process 1480
[Tue Feb 26 11:28:35 2008] [notice] Child 1480: Child process is running
[Tue Feb 26 11:28:35 2008] [notice] Child 1480: Acquired the start mutex.
[Tue Feb 26 11:28:36 2008] [notice] Child 1480: Starting 10 worker threads.
[Tue Feb 26 12:31:29 2008] [notice] Parent: Created child process 552
[Tue Feb 26 12:31:30 2008] [notice] Child 552: Child process is running
[Tue Feb 26 12:31:30 2008] [notice] Child 552: Acquired the start mutex.
[Tue Feb 26 12:31:30 2008] [notice] Child 552: Starting 10 worker threads.
[Tue Feb 26 12:55:12 2008] [notice] Parent: Created child process 1496
[Tue Feb 26 12:55:12 2008] [notice] Child 1496: Child process is running
[Tue Feb 26 12:55:13 2008] [notice] Child 1496: Acquired the start mutex.
[Tue Feb 26 12:55:13 2008] [notice] Child 1496: Starting 10 worker threads.