Please check the configuration in the Commserver for this database. Typically when a database backup is configured to use a recovery catalog, the sys account is not used for the recovery catalog user. This is because the sys account is typically "sysdba". Please check with your DBA to see if the RMAN user in the catalog was given sysdba privileges.
Usually the recovery catalog owner only needs the following grants: resource, dba, & recovery_catalog_owner.
For more details on this please check the oracle documentation (Specifically the Recovery Managers Users Guide) for more details.
If you do not have a catalog configured in your enviroment then I would highly recommend enabling the "Auto-Backup" option in the instance properties in the CommCell Browser for this database. That will make DR recovery of this database possible without having a recovery catalog.
Ernst F. Graeler
Senior Engineer III