Windows 7: Local user account disappears - Win7 Ult x64

This is on a computer at work (small NGO and I'm the 'IT guy'). We have just upgraded all OS on our desktops and our server (7x desktops XP->7, 1x server 2003R2->2008R2). All is fine with the Server and 6 of the PCs. I have enabled the built in Admin user account and for the 6 working fine that is the only local account (all the rest are domain user accounts). This one troublesome machine needs a local user account (for some specific software that we need which doesn't like roaming user accounts because of it's DRM - I hate DRM!!!) Now forget that the PC is on a domain (because I have tested this while not part of the domain).

I am having a similar issue to these:
missing user account
User Account is Missing!!! Help!!!
Stange Problem - user account disappeared

What has been happening is I set the PC up with the local user account, install the required software (& Adobe Air - which the app requires), reboot, log in to the local account, check that the software works fine, reboot again and WHAM - can't log into the local user account! (The account doesn't appear in the login screen).

The account does not show up in any of the places I would expect it to (Local Users & Groups, Control Panel, Advanced Users, net use, etc) and although the user account files still exist (in C:\Users) the folder is owned by an unknown user (identified by the SID). I cross referenced the SID against the registry (HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\ProfileList) and it is definitely the user account I am after.

Where this becomes gnarly is that the DRM on the software I have relies on the user SID so creating a new account (with a different SID) and taking ownership of the files doesn't work. I need to have that account back! What makes it worse is that I need it tomorrow!

I can use System Restore but as soon as I install the software, following a reboot soon after (could be first or second reboot) the account disappears again.



Things that I expect could be a factor:

• Adobe Air (not sure how this could be affecting it?)
• The software I'm installing (again not sure how this could be)
• Windows updates (updates re on Auto - following a sys restore I set them to manual and installed just 2 of the ones waiting, I installed them, rebooted, user account gone, sys restore rollback (ie uninstalled updates) but account still gone)

I have found enough reports of this problem to know that there is something not quite right somewhere, but no one seems to have got to the bottom of what is causing it and how to properly repair it (all 'solutions' are more workarounds rather than actually fixing the problem with the disappearing account).

I would really appreciate any input at all - thanks!