By default, No GC Logon limits the number of updates it can process in any single attempt to 500 objects. This helps to prevent excessive traffic in environments that have configuration problems with replication.
The group membership cache refresh task has reached the maximum number of users for the local domain controller. Maximum number of users: %1
Consider increasing the maximum limit by changing the following registry value: HKLM\System\CurrentControlSet\Services\NTDS\Parameters\
If you are receiving this message and you expect more than 500 users to be cached on this domain controller, use the registry key that is located in the alert message to increase this limit.
If you do not expect more than 500 users, manually identify which site the unexpected users belong to. With that information, you can determine why the Active Directory® directory service is associating those users with this site. Then, you can correct the configuration problem.
For more information, see:
Microsoft Help and Support for Microsoft Windows Server 2003
Microsoft Knowledge Base