Rman backups not deleting from tape

We are having an issue with 10.2.0.3 rman backups not deleting from the tape drive. Here is the rman script that we are using:

run {
   allocate channel ch1 type 'sbt_tape' parms 'ENV=(TDPO_OPTFILE=/home/oracle/rman/tdpo.djjsp1.opt)' CONNECT sys/xxxxxx@djjsp1;
  sql 'alter system switch logfile';
  sql 'alter database backup controlfile to trace';
  backup recovery area
   format 'df_%t_%s_%p';
   delete force noprompt obsolete;
   release channel ch1;
}
 

Any clues or help would be appreciated.