I have an end user getting the following message whenever trying to connect to our Windows PPTP VPN:
Error 651: The modem (or other connecting device) has reported an error.
I've performed a number of steps and still haven't been able to resolve the issue. So far I have tried:
Checked for installation of Microsoft Virtual PC or VirtualBox as others have reported problems with these, but neither are installed.
Disabled IPv6 for the connection source.
Recreated VPN connection.
Reinstalled NIC drivers.
Disabled Windows Vista/7 auto-tuning feature source.
Disabled antivirus and Windows Firewall.
Checked router for any problems or firmware updates (there were none).