OEM 10g2 Database Control can't stop/drop/change a MGMT job from the job activity list

 There is a job in the job activity list (from database instance homepage -> jobs, not administration -> jobs!) that has the status "planned"
with a date in the past - how this was achieved is unknown.

I tried to stop and/or to delete or to change it without any success!
After stopping came an confirmation message, but when I call up the job activity list again, the status is unchanged "planned"!
When I try to delete than an error message appears, that says the job is still activ. But the status "activ" can't select from the status menue!