remove duplicate the backup set

Hi,

I having an issue with the removing of a backup set that was made by fully patched BE 15. I had a tape with the different backup sets of my Hyper-v machines. 3 month ago I did duplicate the backup set of one of the VMs to a disk storage. some times ago we did rewrite the Tape that has the oraginal VM backup set and now the duplicated backup set on the disk storage also shows Expire in blue color but the backup sets is not removed from the storage disk. I even run the expire manually but nothing happens and the files are still on the disk. this backup set has no dependencies.

How can I remove the files from the Disk storage? is this has something to do with the DLM?

Thanks