Database Software

This is what I'm doing:

allocate channel c1 type 'SBT_TAPE';
allocate channel c2 type 'SBT_TAPE';
allocate channel c3 type 'SBT_TAPE';
send 'NB_ORA_POLICY=solktxes214_Oracle, NB_ORA_SCHED=man_log';
backup
format 'log_t%t_s%s_p%p'
(archivelog all delete input);
release channel c1;
release channel c2;
release channel c3;


and this is the result:

RMAN-03009: failure of backup command on c1 channel at 06/10/2011 00:01:16
ORA-19506: failed to create sequential file, name="log_t753408000_s10111_p1", parms=""
ORA-27028: skgfqcre: sbtbackup returned error
ORA-19511: Error received from media manager layer, error text:
VxBSACreateObject: Failed with error:
Server Status: cannot connect on socket
channel c1 disabled, job failed on it will be run on another channel

. . . .

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================

RMAN-03009: failure of backup command on c1 channel at 06/10/2011 00:01:16
ORA-19506: failed to create sequential file, name="log_t753408000_s10111_p1", parms=""
ORA-27028: skgfqcre: sbtbackup returned error
ORA-19511: Error received from media manager layer, error text:
VxBSACreateObject: Failed with error:
Server Status: cannot connect on socket

This is the same for all 3 channels c1,c2,c3

This has been working for several years until about 3 days ago. My system crashed and SB2 is disabled(dead).

Where are these channels?
What do they mean?
Does the system board crashing have anything to do with this?
How can I reallocated to channels on SB0 or SB4?

Any help is greatly appreciated.

Thanks