The best way to determine the error is to try it yourself. In the reputation page I clicked(try to expand) the arrow (collapsible fieldset) in a certain day and pawn an error like this:
Error occurred when loading post body.
I tested it on Chrome and Firefox.
I also tested it on the following sites:
- Anime & Manga
- Meta Stackoverflow
- Server Fault
Now, I assume that this happens to all stack network to all browsers though I haven't tested on mobile/tablet device yet.