Way to reproduce:
1. Open XF in IE 8/7 and Click on Post New Thread. After TinyMCE editor loads, click on the Insert Image/Insert Video buttons.
3. This is the error prompt,
4. And here's the error
Webpage error details User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0) Timestamp: Sun, 26 Jun 2011 06:52:46 UTC Message: 'undefined' is null or not an object Line: 724 Char: 5 Code: 0 URI: http://xenforo.com/community/js/tinymce/themes/xenforo/editor_template.js?_v=170916bd
I did some research and a stray comma in the editor_template.js code *may* be the cause. This is annoying as inserting images/vids in IE is not possible.