Vista has a long history of problems with AV programs, and it appears Avast is the latest victim.
After this morning's automatic update, my computer hung up. I manually restarted it, but after about 5 minutes it hung again. This is the problem I was having:http://www.vistaforums.com/Forum/Topic13079-9-1.aspx
The symptom is that the system gradually hangs up, with the disk activity light continuously on. If you press <ctrl-alt-delete>, after about a minute an error dialog appears with this title:
"Login process has failed to create the security options dialog." and dialog message "Failure - Security Options".
My solution was to boot to Safe Mode and uninstall Avast. This has apparently cured the problem, with no hangs in the 1.5 hours since I uninstalled.
Obviously having no AV program isn't an option, so I'll reinstall Avast without the latest update.
I'm running a Dell Inspiron 1525, Vista with all updates (but not SP1), Avast setup file version 4.8.1201.0 and today's update.