How to fix strange 500 Error after Editing Menu?

Question

I have strange situation which just started which I seem to be unable to resolved. I am not sure what this might be related to but I think I remember reading somewhere that this has happened to someone else.

Upon logging into WordPress then going into the menu management area, then clicking on "screen options" and enabling the view of a menu metabox for a custom post type that was created and then adding a page from that post type to the menu the menu management area started showing a Internal Server Error 500 message.

Every other area of the website and admin area works perfectly except for the menu management link. I have attempted everything I can think of in an effort to resolve the problem including removing every plugin and customization made to my functions.php file however I can't get the issue resolved.

I was hoping someone here might able to help me resolve this issue or suggest anything to diagnose this issue.

Any help is greatly appreciated!

Answer 1

I just figured out my own issue which I am hoping might help others if they get stuck in this situation.

Essentially the problem seemed to be that modsecurity caused the 500 Internal Server error because for some reason (which I have yet to understand) the menu page was sending a bunch of data in the response body.

To resolve the problem I just needed to add the following to my vhost.conf file and restart apache. Here I doubled the response body size.

SecResponseBodyLimit 1572864

Answer 2

I experienced the same problem. For some reason WordPress inserts the complete text of the post into the description of each menu element, making it very heavy to upload when there are several elements. Just modify (shorten) or delete this description and changes will be saved with no 500 error. It worked for me.

Answer 3

I got around this by updating the menu via Appearances > Customise > Menus