You must take special care when removing a volume from a copy pool backup storage group. Before doing so, you must ensure that the volume is not the target of a valid DFSMShsm backup version. You can verify this by examining the output from the DFSMShsm LIST COPYPOOLBACKUPSTORAGEGROUP command.
If a target volume needs to be removed from a valid source to target pairing, you should use the FRDELETE command to delete the DFSMShsm backup version that the volume is a part of before you remove the volume.