dns problems

All of my clients which are Windows 2000 prof. on my NT network run McAfee ASAP. This program updates dat files to the clients by going to a McAfee site and downloading automaticlly at login/reboot. I have never had any problems and now after installing dns on my NT server I sometimes have problems. The reason I suspect dns is because if I stop and restart the service then my clients get logged in and there McAfee updated. Any suggestions what to check or do out there THANKS…