Erasing LTO tapes

We have a Powervault 110T external tape drive attached to our Dell Powervault 745N file server. We have 10 tapes. One tape goes in each day and a manual back up of the entire hard drive is done. This gives us 10 days (M thru F over two weeks) of full backups. Once two weeks is over, we start with tape #1 and overwrite it. Make sense? We are using MS Windows 2003 Backup software.

 

This used to be the job for my assistant. He is now gone. I popped in Tape #3 today. The backup fails. I figured I would erase the tape or somehow mark it as free but I can't find any way to do this. I did make it to the Restore and Manage Media tab and looked at my list of tapes. There are only four. Those are the original backups we did on this machine months ago when we first acquired it.

 

I have no idea what's going on here. There is obviously something on this tape and the others. How can I established them as available so that I can do backups? Any suggestions?