I had the same trouble on AIX. Check that Connect Agent's password file
(ADSMO.xxxx) is in the directory pointed by DSMI_ORC_DIR and  that its name is
ADSM.<DSMO_NODE>. This works:
       run
       {
       allocate channel t1 type 'sbt_tape' parms
       'ENV=(DSMI_ORC_CONFIG=/usr/lpp/adsm/api/bin/dsm.opt,
       DSMI_ORC_DIR=/usr/lpp/adsmagent/aob,
       DSMI_CONFIG=/usr/lpp/adsm/api/bin/dsm.opt,
       DSMI_DIR=/usr/lpp/adsm/api/bin,
       DSMO_NODE=sistemas_oracle,
       DSMO_AVG_SIZE=1000)';

       backup
       filesperset 20
       format 'df_%t_%s_%p'
       (database);
       }


  Hope this helps.
  Carlos