What is configured for append time and did you configure the job to use appendable media?
Sounds like the job waits for appendable media, does not find any and then uses the new or overwritable media, when it is available.

Information about creating media sets and the append time:

http://seer.entsupport.symantec.com/docs/299050.htm

Information about default backup options and media overwite protection (use appendable media):

http://seer.entsupport.symantec.com/docs/309489.htm

So you should make the media appendable and configure the job to use appendable media at first (Append to media, overwrite if no appendable media is available)

best regards

Dominik

If this answers your question or solves your problem, I would appreciate if you mark my post as the solution. Thank you.

Thanks for your reply!

The job was setup like:
 - When job begins: Overwrite media

And the media as:
 - Overwrite protection: overwritable
 - Appendable until: Infinite - allow append

This should according to my logic simply overwrite the tape but I'm apparently wrong. Now I set it to "append to media, overwrite if no appendable media is available". I'll get back to you on this tomorrow and tell you the results...

Try setting the OPP down by one day  That is for tapes overwritten every week on the same day, use an OPP of 6 days, not 7 days

Still no luck. And the overwrite protection period was set to 1 hour!