Error 781 No Valid Certificate W2K VPN

I have probably 50 VPN users who connect to a PPTP VPN server (Win2K sp3). All of them are fine except for one.

This user, when he launches the Connectoid for the VPN he immediately ( as in the moment it displays anything) gets an error 781 No valid certificate error.

Thinking it might be trying to negotiate L2TP, I opened the connectoid and set it to only negotiate PPTP. When I do this, then the connectoid complains about no available modem.

I’ve checked IP filtering rules, IPsec settings, etc. I can use VNC to take control of this remote machine (which connects via dialup), but no matter what I do, I cannot get the VPN connectoid to do anything but error out.

Any suggestions?