What messages did you get in the activity log?
It could be a number of problems.
Are the session limit parameters correct?
Are there tapes in the primary tape pool that you are sending to (is it a
primary pool).
I presume when you say copy pool you mean next storage pool which is a tape
(sequential) primary storage pool.  Usually when I have this problem it is
something dumb that I just forgot to key in.

The other piece is the database estimated element support did not come into
play until recently which will be needed if you want to cause it to fail
over to the tape pool if it is too large for the disk pool.  Did you set a
maximum threshold on the primary disk pool?