This is on a RHEL 5.7 x86_64 system; an old stgpool volume on external storage 
failed, so I marked it "destroyed", and then tried to run

del vol /the/volume/name discarddata=yes

That fails with

ANR2017I Administrator ADMIN issued command: DELETE VOLUME /TSM_POOL/19/data19
discarddata=yes
ANR0984I Process 1836 for DELETE VOLUME (DISCARD DATA) started in the
BACKGROUND at 01:19:56 PM.
ANR2222I Discard Data process started for volume /TSM_POOL/19/data19 (process
ID 1836).
ANR9999D_2990890315 PrepareClusters(dftxn.c:875) Thread<22998>: Logical
occupancy went negative for Pool 25, Ck1=75, Ck2=1.
ANR9999D Thread<22998> issued message 9999 from:
ANR9999D Thread<22998>  0x00000000b95ba2 OutDiagToCons
ANR9999D Thread<22998>  0x00000000b986a9 outDiagfExt
ANR9999D Thread<22998>  0x00000000610e01 DfPrepareTxn
ANR9999D Thread<22998>  0x000000005e05a1 bfPrepareTxn
ANR9999D Thread<22998>  0x00000000b682c1 CollectVotes
ANR9999D Thread<22998>  0x00000000b686b4 tmEnd
ANR9999D Thread<22998>  0x000000004b220c AdmVolDelThread
ANR9999D Thread<22998>  0x00000000c01af4 StartThread
ANR9999D Thread<22998>  0x000039ba00677d *UNKNOWN*
ANR9999D Thread<22998>  0x000039b94d325d *UNKNOWN*
ANR1181E dftxn.c(212): Data storage transaction 0:3.186769174 was aborted.

Any ideas?