RMAN-06004: ORACLE error from recovery catalog database
                                                 Last update (2012-07-23 19:30:58)
                                                                                                                   Date added (2012-07-23 19:15:35)

Summary
When trying to upgrade the RMAN catalog from 11.2.0.1 to 11.2.0.3 with the command:

RMAN> upgrade catalog;

I get the error:

error creating upgcat_fix_plugin_scn_in_ts_and_tsatt
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-06004: ORACLE error from recovery catalog database: 
ORA-02292: integrity constraint (RMAN.DF_F5) violated - child record found

The upgrade catalog process stops with error and the RMAN catalog is incomplete with invalid objects. It is not working.
When i try to connect from another database and use the RMAN catalog i get the message:

RMAN-06429: RCVCAT database is not compatible with this version of RMAN

Workaround: Drop the constraint RMAN.DF_F5 and re run the upgrade catalog command again.
The script will finish successfully and will create the same referential constraint with a different name.