Do you have ICMP disabled on your border routers? Group Policy Objects use the Internet Control Message Protocol (ICMP) to detect slow network links. Group Policy uses ICMP to detect slow network links. The remote-site workstations are having difficulties logging in because the GPO is attempting to transmit all GPO settings over the slow link rather than withholding scripts, Software Installation and Folder Redirection settings as is the default behavior over slow links. If your network configuration involves any hardware or software-based firewall solutions, you will need to enable ICMP packets between your controllers and clients.
This was first published in January 2004