DFSMShsm has attempted to add a tape volume volser that already contains valid data.
The tape volume is rejected and DFSMShsm processing continues.
Issue a LIST TTOC (volser) command to determine what valid data exists on the tape. If the data on the tape volume is no longer needed, issue a FIXCDS DELETE command to delete the TTOC (tape table of contents) records for the volume. Then issue the ADDVOL command again. You can find a description of the FIXCDS command in the z/OS DFSMShsm Diagnosis.
DFSMShsm