Oracle Server - Enterprise Edition - Version: 9.2.0.7 and later [Release: 9.2 and later ]
Information in this document applies to any platform.
***Checked for relevance on 27-Dec-2011***

Symptoms

RMAN backup of database using Veritas MML failed with below errors:

released channel: T1
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of backup command on T1 channel at 02/24/2008 09:26:47
RMAN-10032: unhandled exception during execution of job step 1:
ORA-19583: conversation terminated due to error
ORA-27206: requested file not found in media management catalog
ORA-06512: at "SYS.DBMS_BACKUP_RESTORE", line 625
ORA-06512: at line 579
RMAN-10035: exception raised in RPC:
ORA-19583: conversation terminated due to error
ORA-27206: requested file not found in media management catalog
ORA-06512: at "SYS.DBMS_BACKUP_RESTORE", line 625
RMAN-10031: RPC Error: ORA-19583 occurred during call to DBMS_BACKUP_RESTORE.BACKUPPIECECREATE

Cause

The MML parameters like NB_ORA_CLIENT and NB_ORA_SERV were not given 
in proper case while configuring channel in RMAN backup. These parameters are case sensitive.
RMAN>ALLOCATE CHANNEL ch00 TYPE sbt_tape;
send 'NB_ORA_CLIENT=<NetBackup_client> NB_ORA_SERV=<NetBackup_master_server>';

Solution

The NB_ORA_CLIENT and NB_ORA_SERV MML parameters are case sensitive. 
So make sure to give these parameters in same case while allocating or configuring RMAN channel as it is configure in Veritas server.