Zip drive won't eject disk

I have an older zip 100 USB drive that is connected to my G3 iMac DV+. Tonight I've run into a problem that I've never encountered before and wanted to get some input and advice from someone on the forum.

My problem is that I use the zip disks to back up individual folders in my home directory (everything except music, movies, and pictures are under 100mb). This has worked nicely as a backup strategy until tonight, when two different disks have refused to eject after the file copy was done. The Finder gives me a message that "The disk (diskname) is in use and cannot be ejected. Try quitting applications and try again."

I don't have any other applications running! Right now I only have Finder, Dashboard, and Safari, none of which should be doing anything with the disk.

I have rebooted, used Disk Utility (which doesn't see anything wrong with the disk) and even tried the Iomega Tools (which doesn't have an "eject" function, duh!).

I've read where some folks have had problems with Zip drives in Tiger, is there a documented issue? Or is this something that only I am faced with?

Any help or advice appreciated!