Microsoft Knowledge Base Article 887303 contains the following summary:
You may experience one or many errors and events if Group Policy is applied to the computers on your network. To determine the cause of the issue, you must troubleshoot the configuration of the computers on your network. Follow these steps to troubleshoot the cause of the issue:
1. Examine the DNS settings and network properties on the servers and client computers.
2. Examine the Server Message Block signing settings on the client computers.
3. Make sure that the TCP/IP NetBIOS Helper service, the Net Logon service, and the Remote Procedure Call (RPC) service are started on all computers.
4. Make sure that Distributed File System (DFS) is enabled on all computers.
5. Examine the contents and the permissions of the Sysvol folder.
6. Make sure that the Bypass traverse checking right is granted to the required groups.
7. Make sure that the domain controllers are not in a journal wrap state.
8. Run the dfsutil /purgemupcache command.