tape labelling / cloning issues

Dear Experts!

Our customer using Networker 9.1.We are saving data to the DD and after that

customer clone the data to the tape.Customer is changing the tape every weekend

and overwrite the tape after 3 weeks.However a few months ago the following error occured:

If we put the tape back to the jukebox which tape is:

0% used, and status is appendable

The NW doesnt want to use this tape.It is asking a new tape for this pool.

We can do to things:

- delete the tape from the media index, and label again.

  (then loads the tape and doesnt complains another one)

- label the tape but it says: 

  duplicate volume id, choose a new name or delete the original one and

  or:

  expected volume id yyy got xxx

   Sometimes the labelling work.

Previously the simply relabelling is worked well.

No change in the pool configuration.Question:

- How can we fix this problem? Deleting the tape is time consuming.

- Any ideas?

Thanks in advance.

BR:

Pal Szabo