Essoman~
Quite a few things things could cause this error..
Everything from Uninstalling a program or a driver to a possible malware/virus infection..
I'm sure other will chime in here with links and such to help with (if it is the case) malware/virus removal.
I would suggest a couple things.
>Check you recycle bin for the file .. sometimes it ends up in there.. and then restore it from there.
> Go the most recent system restore point BEFORE this issue seemed to happen( If you remember).
> depending on the "error message" it MAY show what program needs that file to run. IF it does .. you can try reinstalling that program.
*** Edited to add***
> Check you drivers .. whether you have changed any hardware or not .. make sure ALL of your drivers are up to date.
Those are just SOME ways to find a resolution to your problem.
Good Luck.
~LoneWolf