windows 8 file history does not recognize my iomega hard drive

Ok, I've now cracked the problem of File History not recognising my external USB expansion drive, even though the drive had worked initially and it was behaving normally in File Explorer. Here's how I did it - it worked for me on my PC - maybe it will work for others.

1. Open File History and click Select Drive. Select a different drive than the one that is failing to be recognised. (If necessary add an extra internal HDD to your PC. If you have a laptop you could try adding an additional external USB drive to a different USB port - I haven't tried this.) Proceed to set up File History on the new drive. Then turn File History off on the new drive so that a whole lot of your files are not transferred there.
2. Go to the external USB drive that wasn't being recognised, find the File History folder and rename it to "File History.old" or delete it.
3. Go to your C:\Users\your user folder\AppData\Local\Microsoft\Windows, find the File History folder and rename it "File History.old" or delete it. 
4. Re-open File History, click Select drive and select the original USB drive that was not being recognised. The drive should now set up normally and start operating. 
5. Delete the File History folder on the spare drive used in procedure 1. above.

The above process is relevant to situations where people may have altered drive letters by adding or removing drives or moving the system between drives and because of this the File History configuration files are pointing at the wrong drive.

I  don't know if this will help anyone else, but I spent 3 hours two nights ago on the phone with the MIcrosoft "Answer Desk":   

http://answerdesk.microsoftstore.com/

I don't remember how I found them, but I'm glad I did.  It started as a chat session, but then the agent offered to remote my computer and he took it from there.  He did a ton of different things, and was also editing the registry, and updating driver files on my ext device.  But ultimately, what seemed to seal the deal was when he reassigned the name of my external device with a different drive name.  Apparently, my second device was carrying a different file name than the first drive I had connected.  He changed the drive name to be the same as the drive that File History kept looking and asking for, and voila...it worked.  He said it tricked the registry into thinking that it was getting the same device.  I'm not sure it was all as simple as that, but whatever he did worked.  He told me that since I had purchased a new computer with Win8, I was eligible for "warranty" service at no charge.  What a nice surprise that was.  So if you are also in that boat...having just gotten Win 8 or moved up to it, it might be worth a shot to bring up the Microsoft Answer Desk, and start a chat and see where it goes.  For me it was a Godsend, because my next option was to reinstall the operating system with my recovery disk, and I sure didn't want to go through all that.  Good luck all...there is hope if you can get to the right person!