Apar PQ09463 covers a similar problem.  I had opened an ETR with IBM on
receiving the ANR0522W Out of Space condition for writing to a tape storage 
pool -
that had PLENTY of scratch tapes available, I might add.  They lumped my problem
in with PQ09463 (which might be fixed at this point).  IBM stated that when the
server is trying to write a transaction, it will try two volumes only - and if
unsuccessful in finding space in those two volumes will fail with the out of 
space
condition.

     Is your disk pool split into numerous individual 'volumes'?  Is it possible
that some of those volumes are nearly full, but the disk pool as a whole is only
9% allocated?

                         Ginny