Hi Hugo,

>>Has a network administration policy (possibly via a Group Policy Object) been set that forces the logon screen to appear after X minutes of inactivity?
>I searched all the policies and I could not find any. Interestingly enough is that we have several other computers (I think you visited the computer room) and this is the only one mis-behaving.

Yes, I think I know the computer(s) you're talking about.

Is it possible there is a process that, once in a while or on a regular schedule, needs to or tries to access a file that is not accessible with the permissions of the logged-on account? IIRC in some cases you use RunAs for apps or processes, I'm wondering if some periodic process needs more permissions or to be RunAs another user.

Along the same lines, is it possible there is a scheduled process, that is run under a certain account/password combination, and that password has been changed? You may need to update the password in Scheduled Tasks if so.

You have turned off all power saving and set device shutdowns to "Never". That's good - have you also set System Standby to "Never", and disabled Hibernation on the Hibernate tab?

If the machine has a UPS, is it possible the UPS battery is failing, and causing spurious power events to be processed on the computer? Lead-acid gel cell batteries in typical UPSs are good only for about 5 years (similar to car batteries). UPS monitoring software might be forcing Standby or Hibernate modes if so configured.

A SWAG - you could try purposely turning on the password-protected screen saver, letting it time out, logging back on, then disabling the password-protected screen saver again. This might help if there's some inconsistency in registry settings behind the scenes.