ORA-27027: sbtremove2 returned error

hi, everyone:

   who can help me ?

  when i try execute backup a task , how to solve it ?

channel d2: starting piece 1 at 15-OCT-11

released channel: d1

released channel: d2

RMAN-00571: ===========================================================

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

RMAN-00571: ===========================================================

RMAN-03009: failure of backup command on d2 channel at 10/15/2011 09:18:48

ORA-19509: failed to delete sequential file, handle="FULL_DBEAS_3lmp5apj_1_1", p

OUTPUT

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arms=""

ORA-27027: sbtremove2 returned error

ORA-19511: Error received from media manager layer, error text:

   Permission denied, user 'oracle' on 'backup2' does not have 'Operate NetWorke

r' privilege to 鎵ц姝ゆ搷浣?- NSR.

(2:2:11)

ORA-27191: sbtinfo2 returned error

Additional information: 3306

ORA-19511: Error received from media manager layer, error text:

OUTPUT