Hi, thanks for your quick reply.

I have tested it in IE7,8,9, FF4, chrome. Please note all examples work fine on all these browsers. Yes, I can delete 'undefined' and use the editor just fine but would really like to solve this problem.

I have noticed that 'undefined' doesn't appear when editing an equation. The difference in url is the querystring where latex is added to the end with 'undefined' even when menu icon is clicked to insert a new equation, see below

http://latex.codecogs.com/editor_json3.php?type=url&editor=FCKEditor&lang=en&latex=undefined

http://latex.codecogs.com/editor_json3.php?type=url&editor=FCKEditor&lang=en&latex=%5Cbigcap

whereas on clicking the menu icon on one of your examples produces http://latex.codecogs.com/editor_json3.php?type=url&editor=FCKEditor&lang=en

Hope this helps.

thanks