Hi

C:\>rman target sys/password@tsh1 rcvcat rman/rman@dba1 msglog 'C:\Oracle\Backup\TSH1\TSH1_Daily_Backup.log'

Recovery Manager: Release 8.1.7.0.0 - Production

RMAN-06005: connected to target database: TSH1 (DBID=955315395)
RMAN-06008: connected to recovery catalog database

RMAN> register database;

while connected to the target database through recovery catalog you should explicity register the database in the recover catalog..

http://www.oracle-base.com/Articles/8i/RecoveryManager(RMAN)8i.asp

The article is by one of our members Tim Hall refer to his site..

regards
Hrishy