Download ClamXav (it's free) and do a complete scan of your system. make sure it downloads the latest definitions (it should do that automatically.) So just to be on the safe side, we'll cover the malware issue.
If that turns up nothing, we'll consider some other things.
Also, check the permissions on that file.
Have you tried creating a file of the same name on a different volume and then overwriting that one? (not sure if that trick works, maybe only on Windows . . . )