I think it was a memory limit on the server I had it set to 128M and ended up trying another classified plugin before adjusting the memory limit WPAdvert https://wpadverts.com/ which I think will do the job, after I installed the Knowledge base plugin you recommended I noticed the 500 error again, I took the server to 256M and the error went away, I decided to leave it at 512M since I have plenty on my VPS. That said I have not tested the original classifieds plugin I was working with, though I still think it has some strong features out of the box.