Back-up Exec Tape Folders Empty When Expanded

Hi,

I have a back-up tape I have carried out numerous restores from on backup exec 11d. One day I ran inventory on the tape to another restore but when I tried to expand the folders to select the files I wanted to restore, the folders where empty. All the folders have a white circle with a ? in it. All the data is still on the disc and the tape is showing as not having been modified since the back-up was origninally done.Can you help me please?

Thanks,

Seamus