ORA-02800 when starting a scheduler job

Say you are playing with Oracle Scheduler and you are trying to start a job. Everything is working all right. The remote scheduler agent is upgraded to the latest patch level, the certificate is fixed and the scheduler agent is running.
Everything looks OK and still you are greeted with a happy ORA-02800: Requests timed out.


Before pulling your last hair, take a look at the status of the scheduler:

As you can see, the scheduler is disabled and the job start request did not even reach the remote scheduler agent. Regular jobs will also get this error when the scheduler is disabled in this way. Enable the scheduler

and this problem will be solved and your job is free to run.