the tap-win32 adapter is not part of any trusted network and hence domain access is not allowed. Try this suggestion from
http://www.tomshardware.co.uk/forum/28594-17-windows-unidentified-network after the VPN has come up:
- run a CMD.EXE as administrator / with elevated privileges
- type:
route delete 0.0.0.0
- now try to make the tap-win32 adapter a trusted (private or work) adapter