Normally this would be a windows 10 problem because the MS-CHAP v2 is not enabled. It’s on the security tab of the VPN properties. However, I had one user encounter it and the protocol was enabled. Turned out they were using a wireless extender in their house and it would not properly deal with the security protocol. In the future I’m going to require our home users to hardwire to the Ethernet port on the home router and test the connection before going to a lot of trouble getting my hands on the unit.
Follow up. Witnessed another laptop exhibit the same error. This one happened as the user switched wireless access points while the VPN was attempting to connect. The first WAP had a delayed response so the user switched to one that was better and got an immediate security layer failure.
Jerry's blog 