ORA-4031 error

 I see the following error in alert log. Please guide me as this was happened in production now.

Errors in file d:\oracle\ora92\admin\<sid>\udump\voyoper_j002_6672.trc:

ORA-04031: unable to allocate 20836 bytes of shared memory ("shared pool","unknown object","sga heap(1,0)","session param values")

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error in trace file:

error 4031 in job queue process
ORA-04031: unable to allocate 20836 bytes of shared memory ("shared pool","unknown object","sga heap(1,0)","session param values")
OPIRIP: Uncaught error 447. Error stack:
ORA-00447: fatal error in background process

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My DB version: 9.2.0.8

Sahred pool: 256 MB

Buffer cache: 10937 MB

Large Pool: 16 MB

Java pool: 152 MB

SGA: 11363 MB