Pier wrote
But the ADSM connect agent does have to be installed on the target database or
on the rcvcat database? Because I' ve installed it on the rcvcat database
(8.0.4) only.

Pier,  We have this installed on all of the nodes (UNIX clients) that we connect
to target oracle instances on.  You will need to relink ORACLE and the ADSM 
Oracle
Backup Agent.  I would recommend doing this when ORACLE is stopped.  Others may
have opinions on this.

Also, make sure you log on to MetaLink NOTE: 73431.1 and check the "RMAN
compatibility matrix".  There are some problems, like:
8.1.5  rcvcat backs up 8.0.4 and 8.0.5 databases wonderfully.
    However, it cannot restore them!!!!! (bug# 893864)

We found a number of bugs with 8.0.4.3.1 RMAN and ADSM 3.1, yet I don't remember
if they were related to Oracle Parallel Server (not Parallel Query).
We upgraded to 8.1.5 to get to a more solid RMAN product.
Consider being on the newest 8.0.6+ or 8.1.6 for rcvcat.
See the matrix for more information.

Gale