This also happened to me, I would setup the VPN and it would work one time but once you disconnect it would not connect again. If I went back into the Windows settings it changed "Username and Password" to "Generic Authentication Method" which is incorrect and turned PAP off. The solution that worked for me is: Wipe out the VPN and re-create it from scratch configured correctly but don't actually connect when done. In Windows there is a tool called rasphone which is an older way to do VPN connections (can be found by searching in the start menu, or going to C:\Windows\system32) When you start the app it pulls any existing VPN connections and after typing in my username and password after clicking connect it not only worked but will not change settings. I created a shortcut to rasphone on the users desktop and just named it VPN, hope this can help someone.
... View more