FAT is corrupted, MAC OS user

I have been having the same problem with my Clip+. I plug it into the Mac Pro and it is not recognized in the Finder or ITunes. So I opened the Disc Utility and followed the directions (which I also did yesterday on my other clip+ and it now works fine). Did all the steps outlined but now the “Unmounting DisK” twirly bar has been running for 30 minutes. How long should this take? Do I just unplug it?