>     Ok, I have successfully configured an auto-tape library and schedules.
>My problem now is I filled the first set of tapes and went to use another
>set. I remove the tapes and put in the new ones. The machine has a barcode
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>reader and I labeled the new tapes. I define a new library and assigned the
>drive tot he library. When I do a query libvol I can see all the tapes.
>But, when I try a backup of any of the clients I get a "server media mount
>not possible" error. What have I missed ????

Sounds like the old tapes were physically removed, without going through TSM,
which is calling for a mount of a previous Filling tape, which the library
tells TSM that it cannot do.  There may be an accompanying message identifying
the tape, which you could check for being in the set of removed tapes.
Also, did you Checkin the new volumes, as Scratch, in addition to labeling
them?