Unable to Publish Post with Images

As stated in title. I get the following error upon Publish, Preview and Save Draft:

Not Acceptable

An appropriate representation of the requested resource /wp-admin/post.php could not be found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

I have tried deactivating all plugins, switching theme to Twenty Thirteen, clearing cache and switching browser, and still so long there is an <img> in the post, the error pops up. I post them from my own media library too.

I am not keen on reinstalling the site again since I spent a while getting the layout and customization done…but if it’s the only thing I can do then I’ll get to it.