Could you tell me more about that sim you were using, their life state and how they got the job? Perhaps we can figure out what exactly it is that causes a sim to become glitched for the career.
I have the exact same problem. My sim is a female spellcaster living in a haunted house, where the ghosts were appearing just fine. She got her licence from Guidry after maxing the Medium skill, and left her previous semi-active career to become a paranormal investigator, except all she does now is wait for dawn because nothing happens at the houses she visits.
My guess is: Either you're not supposed to be a paranormal investigator while also living in a haunted house yourself, or something went wrong while switching careers. But if your sim didn't live in a haunted house or have a different job before, then that can't be it...
