Any one encountered the following?

HP workstation running Vista SP2 x64 with latest Visat/Win7 Client.
Novel Client log in screen comes up, user clicks in password field, types password incorrectly, clicks OK or hits Enter and wha -la!, BSOD.

Power off workstation, power on, boot to log in screen, type password correctly and all is OK.

This is a reproducible event. Each time the password is typed incorrectly the BOSD appears.

Any thoughts on what might prevent this from happening?