Help! Incremental DB backup fails

Hi, we have an incremental DB backup job that is failing using Networker to run rman job.  Logs shows that networker is "unable to find full backups of the save set and recommends a full backup be performed.  We have an oracle client that runs level=0 rman backup(full) which runs on Sunday and skips the rest of the week.  Another oracle client runs level=1 rman backup(incremental) and runs daily except Sunday. The full backup runs successfully but incremental backup has been failing.  Please help.  Thanks.