There is currently a bug where Internet Explorer 8 users cannot reply to existing threads. I am aware of the problem and am still working on a resolution. IE 9 works fine, as do Firefox, Chrome, and Safari. If you are affected, it is highly recommended that you upgrade from IE 8 to IE 9. Regardless, be assured I am currently working on a solution :)
I think i have some bad news for IE8 users moving to IE9 as IE9 don't work well on xp like in vista or windows 7. IE9 required Direct2D for hardware acceleration which is unavailable in windows xp. in my opinion this bug might not have nothing to do with IE8, it might be an script or something. i've been login in to the site from 3 diferent machines, windows xp IE8, windows 7 IE9, MacBook which is running Safari, the only one affected is IE8, and again the "MEMBER LOGIN" issue came back. thank you for your help Dani, i hope everything come to normal again so i continue posting my questions. :-) NOTE: this post is from Safari.
I have just tried with IE8 on XP SP3. I get the message too, but if I select "compatibility view" then it works. When I track the submit, the json returned is data.editor with the message. I think the problem may be in the passed data, perhaps the serializing of the #reply-form.