Question : AD Error: Naming information cannot be located because:

I have a client with a PDC running SBS 2003.
Everyday at 4:30am without fail the AD drops off and Group policy and i get the following error.

Naming information cannot be located because:
The specified domain either does not exist or could not be contacted.
Contact your system administrator to verify that your domain is properly configured and is currently online.

I restart the DC and its fine.  Again 4:30 the next day it will happen again, restart it and then its fine again until 4:30am next day.
At 4:30 the following event is recorded.

SAM, Event ID: 16645
SAM, Event ID: 16651

Any ideas?  This ones got me stuck!

Answer : AD Error: Naming information cannot be located because:

What it can also do is fail if the time fails between clients/servers etc by too large a degree.

Set the sbs to get a good time source and synchronise your systems/wor stations etc