SP1 Blue Screen related to SSTP/VPN?

I have been running Vista x64 with SP1 installed since it was released and
last week I suddenly got a blue screen problem.

The blue screen says SYSTEM_SERVICE_EXCEPTION and reports error code 3B.
I have been able to track it down to soem problem with RASSSTP.SYS and the
crash occurs when the Secure Socket Tunneling Protocol Service is started
about 10-30 seconds after I logon and the desktop appears.

I have temporarily been able to get the computer into a working state by
disabling this service but the RAS Services doesn't run and I need them for
VPN connectivity.

The problem first occured last week after a reboot. I don't know if the
problem is related to some update that was installed at that point but I know
of only two pieces of software that I installed last week: New NVidia drivers
for Latutude D630 and the new Microsoft Virtual PC 2007 SP1. I have tried
uninstalling both of them but the problem is still there.

The device manager shows a set of WAN Miniport network adapters with
problems loading their driver, I assume this is caused by the disabled
services.

Anyone got tips on how to resolve this? I was looking to do some repair
installation or similar but the system restore points on my machine seems to
be broken also.