Problem Restoring from backup tapes

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I'm having a problem restoring selected files from a backup tape. We run nightly backups to a single tape, Monday through Friday, and the tape is changed each day. Each tape is used every other day, and the data from the server overwrites whatever is on the tape when the backup occurs, including the volume label, which the utility updates to one matching the date of the backup. When I tried to search for and restore a single file from one of the backup tapes, the backup utility instructed me to select the tape the file was on by clicking on a gray box next to a list of labels, one of which should have been the backup date I needed the file from. Trouble is, the backup date I needed to restore from was not on the list, even though the backup was only 3 or 4 days old. Interestingly enough, the list did include a backup from several months back. Clicking on a box at the bottom next to a tape icon without a label and inserting the tape I wanted to restore from didn't help either because the utility kept asking me to insert the very tape I had just inserted and then aborted the restore because it couldn't find the tape that I had inserted into the drive just seconds before. Any ideas on what I'm doing wrong?