Hi,
Thanks for posting in the forum.
Regarding the current issue, please understand that this problem may occur if the zone transfer times out because of the load on the Windows 2000 DNS server that is acting as the primary for the zone. The primary server is not correctly handling canceled zone transfer requests. Therefore, it sends multiple zone transfer messages to the same socket, and the secondary server loads an incomplete copy of the zone. At this time, please try to install this hotfix to see if it could help.
Intermittent name resolution issues and event IDs 5501 and 6524 are logged to the DNS server event log
http://support.microsoft.com/kb/330574/en-us
Hope this helps.
Best Regards,
Andy Qi