RMAN backup on tape

Is there somebody who could explain me why my backup doesn't works
I try to backup with RMAN on a tape.

Database server : server1
Networker server : server1
Networker client : server2

When I use NSR_SERVER=server1 , the backup works
But I want to use the Networker client server2 NSR_CLIENT=server2
and this error occur

RMAN-00571: ===========================================================
RMAN-00569: ========= ERROR MESSAGE STACK FOLLOWS =========
RMAN-00571: ===========================================================
RMAN-03007: retryable error occurred during execution of command: backup
RMAN-07004: unhandled exception during command execution on channel t1
RMAN-10035: exception raised in RPC: ORA-19506: failed to create sequential file, name="Backup_full", parms=""
ORA-27028: skgfqcre: sbtbackup returned error

ORA-19511: nwora_index_ssinfo: index connect to server1.com failed for
client server2.com: `server2.com' is not a
registered client

If I remember correctly you need to register the client machine in the Networker Server. I guess the client machine is not registered.