I have a single Wordpress 4.9.16 website that is throwing Error 500s when taking many actions in the admin interface. When I try to do things like add a new category, nothing happens in the front end and my web inspector shows the error.

I have tried:

  • Renaming my .htaccess file and letting WP rebuild a new one
  • Increasing Wordpress memory limit
  • Increasing PHP memory limit
  • Disabling all plugins
  • Re-uploading core files in wp-admin and wp-includes

And after taking each of those steps, I still experience an admin-ajax error 500 when trying to add a category.

My next steps are to either

  • Change my theme
  • Update to 5.6 current release.

I have a few questions, but basically it all comes down to how to fix my admin-ajax 500 error.

  1. If I change my theme to something out of the box (one of the Twenty ______ themes), and then change my theme back to my current theme (a child of Spacious Free), am I likely to experience big problems? Or will most/all of the configurations remain?
  2. Is it likely that I will be able to update to 5.6 if I'm receiving this error? It feels like this is a logical step in diagnosing the issue. I've been holding off because I haven't had a chance to test the site in 5.x, though.
  3. What else should I be looking for?

Thanks. -Ben

  • 1) I think it would preserve the configuration when you switch themes, but if you're worried just take a database backup first.
    – Rup
    Commented Feb 3, 2021 at 9:48

1 Answer 1


Isn't it the case that once you write up what you've tried, you find that one last thing to try that works?

I just discovered that my admin-ajax file had 000 permissions. I reset to 644 and everything started working properly again.

  • Glad you solved it! For the future, you should have been looking at the server's error log for clues where the problem was.
    – Rup
    Commented Feb 3, 2021 at 9:48

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