Thinking it might be useful, I checked the perms and change dates on the three files in this directory, and they haven't changed dates and are 644
library/XenForo/AttachmentHandler
Post.php, ConversationMessage.php, Abstract.php
In fact, no files in the Xenforo directory have had a date change.
The only file that appears to have changed is permissions.xml. I assume obviously that's because I installed, and removed that add-on. I don't have a backup of that file, so I don't really know what it should look like, nor what display_order means, either. I can see in the database there are...
I can't use the attach button, but I can drag files into the reply box and upload that way.
It was working, then I installed an add-on, noticed the next day it wasn't working, removed the add-on, and the problem persists. Ideas? I'm going crazy!
I installed Andy's "change the date of the post"...