Called by the scheduler at the time of the trigger firing, in order to produce a IJob instance on which to call Execute.
the newly instantiated Job
It should be extremely rare for this method to throw an exception - basically only the the case where there is no way at all to instantiate and prepare the Job for execution. When the exception is thrown, the Scheduler will move all triggers associated with the Job into the Error state, which will require human intervention (e.g. an application restart after fixing whatever configuration problem led to the issue wih instantiating the Job.