I have been trying to set up an Xcopy to a removable hard drive to use as my backup medium.

It didn't work smoothly and now I have a situation where the drive thinks there is a directory on it (BackDir) with files in it but they are invisible to Explorer.

Properties shows there to be 2.5 Gb on the drive.
If I try to Xcopy to BackDir it asks if I want to overwrite.
If I do a DOS del *.* on that drive it finds nothing to delete.
It won't let me format the drive because some other process has it open.

What is happening here?

are you running XP and have System Restore enabled on that drive? Or maybe Norton Protected recycle Bin or similar other app?

Yes to XP - No to other two.

The invisible files matter has been fixed by a reboot which allowed me to reformat the drive.

I think it is related to the following:
The Xcopy (in a batch file) doesn't seem to be releasing the removeable (USB) drive after it has finished.
When I go to "Safely remove hardware" Windows says something like "Can't eject hardward at this time. Try again later" but it never does allow it unless I reboot.
I have disk caching turned off.