Thumb drive repair?

I noticed that a few programs on my thumb drive were not working correctly. On a Win7 computer I ran the command prompt and entered chkdsk f: /f --where f: is the volume for the mounted thumb drive.

That returned an error saying the drive was in use by another process and asked whether to force dismount. (There was no reason for the drive to be in use. I checked the running processes and saw nothing that could tie it up, but went ahead and ended all known uncecessary ones anyway. Didn't help.)

I tried Y to force the dismount, but got another error, chkdsk could not run because the drive was in use by another process. This time it asked if it should schedule the volume to be checked the next time the system restarts and I entered Y. I then restarted the system, but the drive was not checked. (Tried a couple of times with no helpful results.)

Somehow I discovered that chkdsk WILL run if I *leave out* the /f tag -- but, of course then it can't fix the errors. If I run it again with the /f tag, I get the "in use by another process" runaround.

So I can't use chkdsk to fix the errors and wonder, does anyone know of a good free utility that will do this? I tried Google but didn't find anything useful; it mostly returned things to repair Windows registries, antivirus scan-and-repair programs, and a couple of for-fee repair tools I can't afford. Not what I need.