If you clients periodically loose connectivity to your PDC via NetBIOS based commands, check the PDC event logs. If you find the following events, uninstall your anti-virus software:

<b>Event ID: 3013
Description: The redirector has timed out to <ServerName>

Event ID: 2022
Source: SRV
Type: Error
Description: The server was unable to find a free connection <number> times in the last <number> seconds.</b>
NOTE: McAfee NetShield has been known to cause this problem.