oracle backup error

During a backup of oracle client the error below is displayed :

savegrp: suppressed 99 lines of output.
RMAN-03002: failure of backup plus archivelog command at 03/31/2011 14:20:41
ORA-19506: failed to create sequential file, name="DDTEST_08m8jtcb_1_1", parms=""
ORA-27028: skgfqcre: sbtbackup returned error
ORA-19511: Error received from media manager layer, error text:
Vendor specific error: OB2_StartObjectBackup() failed ERR(-2)

Recovery Manager complete.
The backup process failed:
RMAN exited with return code '1'.
Exiting with error:
RMAN exited with return code '1'.
fptitivwxpp07:     RMAN exited with return code '1'

Any suggestion to fix the issue ?

Thx

C.