Hi,
Each job requires an initiator thread to run. When job goes from to EXEC state, the agent uses a thread for the job. Thread is released back to agent when job is COMPLETE or FAILED.
You can increase the default initiator, which is set at 1000 to higher number. Increase it only if you see all the threads have used up, this can be checked in
initiatormanager.log.
HTH,
Nitin Pande