After inserting an image using TinyMCE, clicking Preview will show a blank page and never finish loading. Clicking Reply will just toggle the progress bars indefinitely. Switching the text editor to plain text will show a blank page and never finish loading until the image is removed. In quick reply, clicking Post Reply will show the blank page too. Clicking More Options will show Error - This action is available via POST only. Please press the back button and try again. These issues arise regardless if I'm starting a thread, replying, or simply editing a post. It seems to be triggered by images and heavily formatted posts. It's most definitely a local issue (shared server). Turning off mod_security did not help. Any ideas?