Generally speaking, you should not delete virii on first contact. They should be quarantined. That way, if it turns out to be a false positive detection (and almost all the AV's do this at times, even NOD) and a system file was removed, there is a chance to restore it from whence it came.
I believe it's possible this happened in your case.
If it is in the quarantine, try re-scanning it. I understand Esset are pretty good at updating definitions, esp when a false detection is involved. If it scans clean, restore it.
It may well be SP1 playing up; the sequence/timing of events would suggest otherwise.