ntbackup fails "The requested media failed to mount. The operation was aborted."

I got an issue with my SBS, everytime the backup is running I usually get the below error:
"The requested media failed to mount. The operation was aborted."

I have tried to delete C:/windows/system32/NtmsData/* without any hope. The hotfix that microsoft gives is only for use where the backup ends as soon as it starts that it doesnt do here. Can anyone help me out? Thanks

The problem that you are facing is caused by a combination of different events. First the UM switch at the end of your backup job and then second, the data will not fit on one tape, the same combination is not good. So, in this conditions, where the budget is not currently available, what I normally do is not use currently available, what I normally do is not use the SBS built in backup, but create 2 backup jobs. The first backup job runs when someone is available to change the tapes and backs up everything. The second backup job runs every week night and makes a differental backup. If this comes to restore then the last full backup and also the most recent one would be required.

Thanks for the solution, I came to know about that it anyway was because the tape is getting full. But the tapes that we are using is 36/72GB, so the way I see it, is that the tape should be able to hold 72gb compressed data, which it doesnt. Do I manually need to enable compression?