After restarting the RAS services I started to troubleshoot.

I tried everything from disabling/enabling the Miniport driver to deleting the PPTP config and starting again – all to no avail.

Running the Microsoft Port Query tool (http://support.microsoft.com/default.aspx?scid=kb;en-us;310099) I found that the PPTP port 1723 was “ESTABLISHED” – this should be in “LISTENING” mode. This tells me that there is something running on the 1723 port that shouldn’t be – locking my users out.

I then used another great tool from sysinternals to find the process that was using my PPTP port. The tool is called TCPView and you can download it at http://technet.microsoft.com/en-us/sysinternals/bb897437.aspx. TCPView told me that the connection on port 1723 was established by my SQL server and the exe that was using it was a BlackBerry service. I killed the process, restarted the RAS services and our PPTP VPN was now working.