I am having some difficulty/confusion  trying to replicate
multiple databases that exist on the same node.

I have no problem with the following config and it is working.
SERVER1            SERVER2
========           ========
    db1  -------------->db1
(node1)               (node2)

However, I cannot get the following to work (add db).
SERVER1            SERVER2
========           ========
    db1  -------------->db1
(node1)               (node2)    

    db2 --------------->db2
(node3)               (node4)

When I try  
CREATE SET (ID=3, ORIGIN=3, COMMENT = 'Second Node tables');
I get
<stdin>:27: PGRES_FATAL_ERROR select "_slony_rep".storeSet(3, 'Second 
Node tables');  
- ERROR:  Namespace "_slony_rep" does not exist

I have the following as admin conninfo
node 1 admin conninfo = 'dbname=$MASTERDBNAME host=$MASTERHOST 
user=$REPLICATIONUSER';
node 2 admin conninfo = 'dbname=$SLAVEDBNAME host=$SLAVEHOST 
user=$REPLICATIONUSER';
node 3 admin conninfo = 'dbname=$SECONDDBNAME host=$MASTERHOST 
user=$REPLICATIONUSER';
node 4 admin conninfo = 'dbname=$SECONDSLAVENAME host=$SLAVEHOST 
user=$REPLICATIONUSER';

store node (id=3, comment = 'DB2 Master node');
store node (id=4, comment = 'DB2 Slave node');
store path (server = 3, client = 4, conninfo='dbname=$SECONDDBNAME 
host=$MASTERHOST user=$REPLICATIONUSER');
store path (server = 4, client = 3, conninfo='dbname=$SECONDSLAVENAME 
host=$SLAVEHOST user=$REPLICATIONUSER');
store listen (origin=3, provider = 3, receiver =4);
store listen (origin=4, provider = 4, receiver =3);

How do I tell slony to replicate node3 to node4 ?

TIA,
Melvin