I have VPN passthrough open on my Cisco WRVS4400N router with port range forwarding open on port 1723 to my Windows 2003 server running as a VPN server. It has been working fine until this past Monday. It stopped working all together. Our FTP was not working either, so I did a quick router reboot. When it came back up it lost all the settings and went back to factory defaults. I reconfigured the router with all the same settings I had previously. FTP is working fine, but my VPN is giving me and error saying GRE is not open on the router. Event 20209 on my server. I have tried opening GRE on the router even though it was not open before but that is not working. I cannot connect using PPTP either. Since event id is showing the connection on the server, but still failing it looks like something is not configured correctly, but there is not much to configure on the WRVS4400N. Any help out there would be appreciated.
A connection between the VPN server and the VPN client 188.8.131.52 has been established, but the VPN connection cannot be completed. The most common cause for this is that a firewall or router between the VPN server and the VPN client is not configured to allow Generic Routing Encapsulation (GRE) packets (protocol 47). Verify that the firewalls and routers between your VPN server and the Internet allow GRE packets. Make sure the firewalls and routers on the user's network are also configured to allow GRE packets. If the problem persists, have the user contact the Internet service provider (ISP) to determine whether the ISP might be blocking GRE packets.