Same experience with an HP ProBook 4530 / Win 7.
After upgrading from Avast 8.0.1483 to .1489, the laptop presented with exact same symptoms, “User does not exist”.
Safe mode allowed successful login. Had already followed a similar path as suggested by EssexBoy. As wjmkoopman found, the problem returns after reinstalling Avast 8.0.1489.
Tried playing around with the HP Security Manger without success. I did not cycle that installation as the setup and configuration was extensive.
TEMPORARY SOLUTION: Did a Windows Restore back to a day or so before the Avast Upgrade. Will now wait until Avast publishes a solution, assuming one comes.
If anyone has insight on a resolution for the issue, I’d love to hear it.
– tl