i went phisically in front of server (we manage it remotly usually). I found the tape out the device, while the person who change tapes at night told that yesterday he did it successfully.
So tape was in, this mornig was out and BE asked for a writable media. I've re-inserted the tape and the job started... how can it be?
Now I'm trying again with a new tape first, before erasing existing ones.
I did this exact sequence:
1) inserted a new blank tape into device
2) created a new test job, including some dummy folder
3) started job
4) noticed everything was fine, the tape was automatically catalogated as 4M000015 in "media set 1"
So, keeping 4M000015 in device, i started the job scheduled for nights manually. And it seems it's working.
I can't wait it to finish (about 5 hours)... we'll see how it will be tonight, when the same job has to start automatically...
Thank you