Solving error ORA-12545

I have created a new database to use solely for Recovery Manager. I created the rman user, set default tablespace and granted roles and privileges to user rman. I created catalog. But when I tried to connect target database db01 or db02 or db03 I get the error message below.

Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.

C:Documents and Settingszaman>rman target
sys/change_on_install@db02

Recovery Manager: Release 8.1.7.0.0 - Production

RMAN-00571:

===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571:

===========================================================
RMAN-00554: initialization of internal recovery manager package failed
RMAN-04005: error from target database: ORA-12545: Connect failed because target host or object does not exist

C:Documents and Settingszaman>rman target internal/oracle@db03

Recovery Manager: Release 8.1.7.0.0 - Production

RMAN-00571:

===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571:

===========================================================
RMAN-00554: initialization of internal recovery manager package failed
RMAN-04005: error from target database: ORA-12545: Connect failed because target host or object does not exist

C:Documents and Settingszaman
The ORA-12545 error message is your problem. When connecting to the target database, you specify "internal/oracle@db03". The ADDRESS value in your TNSNAMES.ORA file for the "db03" alias is incorrect. Make sure that it specifies the proper protocol, host and port for this alias.