ORA-12537: TNS: CONNECTION CLOSED

As part of my OCM preparation, I have installed Oracle version 9i and 10gR2 respectivelyand also applied patch sets 9.2.0.8 and 10.2.0.3.
Created a test database on version 9i, enabled archived mode in order to practice backup andrecovery scinarios. Thought of having 9i database backup catalog in 10g database.
Therefore, I have created a small database in 10g. A rman user has been created in 10g for 9i databaserman catlaog.
When trying to connect to the rman user from 9i to create catalog, rman was complaining about thecompatibility, although, my 9i version is 9208, I was little bit puzzeled.'
Tried connecting through sqlplus of Oracle 9i to 10g database where I got 'ORA-12537: TNS: CONNECTION CLOSED'
Wasted good amount of time searching on the google and metalink, but, could not done with the error.
Later, I realized that I have listed 10g database SID with 9i listener.Upon moving 10g database SID with 10g listener, all went smoothly and the ORA-12537 gone away.