With Windows Vista Service Pack 1 RC coming out next week for the general public, there are a few issues that they may come up against.
The one that I've run up against is on my Motion LE1700 Tablet PC, when using the OmniPass password login software, this issue doesn't just effect SP1, but also some other updates that have been rolled out over the last year. Typically this can be solved by reinstalling the OmniPass software, however that is a lot of work and below is a quicker solution.
Essentially after some updates are installed you end up with two copies of your user icon on the welcome screen, this doesn't effect functionality, but its annoying and something I spent most of yesterday trying to get around with numerous reinstalls and uninstalls and system restores. Anyway I've cracked what was causing it, and I hear this will be fixed in a future version of OmniPass.
Warning: Altering this section of the registry is dangerous, you can quite literally remove all user icons from the Welcome screen preventing login. You should ensure System Restore has a recent restore point.
You'll need to crack open regedit and make your way to the location below:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Authentication\Credential Providers\
You should have a key containing OmniPassCredProv, this is the one we want to keep.
There should also be a key containing PasswordProvider, this starts with 6f45dc1e (not shown on the image above), this is the default key OmniPass removes when it is installed, and this is responsible for their being an extra user icon, some updates seem to rebuild this entry. I'd recommend exporting this key (just in case you need to import it back if something went wrong), then deleting it and rebooting. That should restore things to how they used to be.