I have been wondering the answer to this question myself and did some
research.  According to the administrator's guide what you did is the proper
way to checkout and checkin a volume to a library.  But, it does not say you
can move the volume to a new library (device class/storage pool).

This is what I am speculating.  You cannot change the device class of a in a
storage pool without deleting and redefining it.  Once a tape has a private
status I am betting you cannot do what you are trying to do.  However, if
the tape has no data on it and you change its status from private to scratch
I am betting you can check it out and back in to a different library.

Yes, this sucks.  Remember TSM manages objects between storage pools.  So,
you can move all the data off a volume easily with the move command.  Then
you should be able to change the status of the volume to scratch and move
it.  I do not know if you will have to run expiration to be able to change
the volume's status.

I have not tried this but bet that this is the situation.

I think there is a requirement here for us to be able to associate a super
device class to a storage pool that contains many libraries and to be able
to change the location of a volume so long as it is in the super device
class.

Maybe Andy has an idea.