If you are using PPTP on your Mac and get an error saying the connection cannot be negotiated, it indicates that something is either blocking the connection or your local equipment does not support PPTP.
The first thing to try is to reboot your Internet router and also your computer and see if that solves the problem.
If it doesn't, then we recommend that you use our SSL service for OS X instead, as this is a more resilient solution and does not require any special support by your router or ISP.
Full instructions for setting up SSL on your Mac can be found here.
Give that a try and if you have any further problems, please send us an email to email@example.com and we will do our very best to assist you.