I saw mention of the ASPNET account. A long (LONG) time ago this was an issue when some dotnet update didn't do something properly. I tried the userpasswords2 thing which fixed it, but created problems if I changed passwords.
I discovered that the update created the ASPNET account, but failed to put an entry in the registry (see the code section below for the registry key, and the bottom entry for the registry dword entry)
I manually put that in and it fixed my problem! I now make that part of my registry file for my unattended installs (It may or may not be necessary, but a few bytes on my install source is sure worth the removal of the worry of this problem).
A few points. Yes I did read the posts about how userpasswords2 did not help the problem. I also read the part about ASP account being deleted still didn't fix the problem.
I'm just putting this here to give some thought and discussion, or maybe help someone else if it doesn't help the one with the immediate problem.
And now for the registry stuff... the bottom line is all I added, I'm just posting the whole registry export so you can compare to mine.
As a side note, putting "whatevertheaccountnameis"=dword:00000000 will cause that account to not be visible on the welcome screen. Further, if you hide all but one account, that "visible" account "should" just auto logon, and then you would need to logout and hit CTRL-ALT-DEL from the welcome screen (switches to old style login screen), then manually type in the user name and password for the hidden account.
Windows Registry Editor Version 5.00