Can’t delete device driver in Vista

After uninstalling Vista SP1 you may get the yellow triangle error for
the wan miniport (SSTP). You can’t uninstall wan miniport (SSTP) or
delete it.

This is the solution:
Use the following commands to be carried out as the user Administrator
(Run as Administrator) from Command prompt (cmd):
netcfg -e -u ms_sstpminiport

You may have to find the course Hardware ID device from the Device
Manager and selecting the Details tab-> Hardware IDs if it is not
‘ms_sstpminiport’ which is causing the problem.

Taken from: Here