Unidentified Error almost every post.

I've been really struggling to post on forums. It took me at least 5 tries to submit my entry to the art competition, and eventually I got it to work by attaching all my files (in file garden) without any alt text. I then tried to submit my creative writing, but I got the error again. I've tried everything. Removing images, changing formatting, and eventually I got so fed up I just screenshotted the entire thing and pasted in 12 screenshots of the text, no alt text, and even still I'm getting the error. Is there something I'm doing wrong or any known trigger for this?