ORA-12012: error on auto execute of job

Environment: Windows server 2003, Oracle 10.1.0.2.0 standard ed.

I am getting these errors for over 2 months now.
------------------------------------------------

They are filling alert.log and generating lot of and .trc . Please help me with explaining whats going wrong with the job or settings.

ORA-00604: error occurred at recursive SQL level 1
ORA-08102: index key not found, obj# 203, file 1, block 1490 (2)
ORA-12012: error on auto execute of job 26
ORA-08102: index key not found, obj# 203, file 1, block 1490 (2)

See attached file with information about job 26 from DBA_JOBS generated using following sql
select sysdate, dba_jobs.* from dba_jobs

It shows a strange values for columns: (next_date is before the current date)

LAST_DATE Date that this job last successfully executed
LAST_SEC The last successful execution started.
THIS_DATE Date this job started executing (usually null if not executing)
THIS_SEC The last successful execution started.
NEXT_DATE Date that this job will next be executed
NEXT_SEC The job becomes due for execution at this time.

SQL that this job is executing:
------------------------------
SQL> desc sysman.EMD_MAINTENANCE.EXECUTE_EM_DBMS_JOB_PROCS
Parameter Type Mode Default?
--------- ---- ---- --------

-Thanks

-D