RMAN-20001: target database not found in recovery catalog

Issue Description:

           While taking the RMAN Backup, its get failed since the database is not registered in the catalog.

Solution :
a)Connect to target Database and RMAN catalog as below:

$ rman catalog rman /rman@rmancat target rmanbkup/rmanup@orcl
Recovery manager :Release on sun Nov 13 03:25:49 2011
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Connected to target datebase:orcl (DBID=5858479612)
Connected to recovery catalog database 

b)Register Database to RMAN catalog:

RMAN>register database:
database registered in the recovery catalog starting
full resync of recovery catalog
Full resync complete