RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of crosscheck command at 04/22/2009 09:56:47
RMAN-12001: could not open channel ORA_DISK_1
RMAN-10008: could not create channel context
RMAN-10003: unable to connect to target database using connect string "system/manager@proddb"
ORA-01017: invalid username/password; logon denied

I issued the show all command in rman to see all the configuration.

RMAN> show all;

RMAN configuration parameters are:
CONFIGURE RETENTION POLICY TO NONE;
CONFIGURE BACKUP OPTIMIZATION ON;
CONFIGURE DEFAULT DEVICE TYPE TO DISK;
CONFIGURE CONTROLFILE AUTOBACKUP ON;
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '/u10/oracle/proddb/rman/hotbkp/proddb.%F';
CONFIGURE DEVICE TYPE DISK PARALLELISM 2;
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE CHANNEL 1 DEVICE TYPE DISK MAXPIECESIZE 8 G FORMAT   '/u10/oracle/proddb/rman/hotbkp/proddb_N1.%U' CONNECT  'system/manager@proddb';
CONFIGURE CHANNEL 2 DEVICE TYPE DISK MAXPIECESIZE 8 G FORMAT   '/u10/oracle/proddb/rman/hotbkp/proddb_N2.%U' CONNECT  'system/manager@proddb2';
RMAN configuration has no stored or default parameters
CONFIGURE MAXSETSIZE TO UNLIMITED; # default
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u01/oradba/product/9.2.0.6/dbs/snapcf_proddb.f'; # default
RMAN configuration has no stored or default parameters
RMAN configuration has no stored or default parameters

I issued the following command to fix it:

RMAN> CONFIGURE CHANNEL 1 DEVICE TYPE DISK MAXPIECESIZE 8 G FORMAT   '/u10/oracle/proddb/rman/hotbkp/proddb_N1.%U' CONNECT  'system/mynewpassword@proddb';

RMAN> CONFIGURE CHANNEL 2 DEVICE TYPE DISK MAXPIECESIZE 8 G FORMAT   '/u10/oracle/proddb/rman/hotbkp/proddb_N2.%U' CONNECT  'system/mynewpassword@proddb2';

Hope this helps.