I had this problem a while back. It is not a fun one to have. I think that the iossue is the cryptographic services.
If the same issues occur with the 757, and the autopilot starts rocking or cannot hold autopilot, it, even with service pack installed, then the cryptographic services are not working. Only way to sort it was by repairing Win7. This may not be the same problem I had, but I think it could be.
Pete