RMAN-20020: database incarnation not set

PROBLEM

rman target / catalog rman@RMAN_CATALOG
RMAN> register database;

starting full resync of recovery catalog
full resync complete
database registered in recovery catalog
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03008: error while performing automatic resync of recovery catalog
RMAN-20020: database incarnation not set

SOLUTION   

$rman target / catalog rman@RMAN_CATALOG
RMAN> unregister database;
RMAN> register database;