Hi again
When you ran your restore procedure, did you do a complete restore, or a custom "partial" restore? Malware can survive the "partial" restores - and rootkits can evade scans, once they've been able to establish themselves in the system. Malware does not usually survive a "complete" restore, as these involve writing a saved image onto the hard drive, overwriting everything underneath.
Make sure to include a rootkit scan or two in your troubleshooting, just to be sure.
When do you see the error appear?
If it appears at startup, then you can look at the programs that automatically start everytime you start the PC. It's likely that if you can find the problem program, uninstalling/reinstalling the program will fix it. You can use the free Microsoft/SysInternals "Autorun" utility to help with this ...
http://technet.microsoft.com/en-us/s.../bb963902.aspx
You can also look in your EventViewer logs for detailed error information --- it's in the Control Panel, in the Administrative Tools.
...It's very late here, and I'm half-asleep - but I'll check in on you a bit later today (I'm too groggy to be very thorough at the moment!) . . .
Best of luck,
. . . Gary