When trying to display a dialog using the new FCKDialog while on IE while in source view an error occurs.
IE says "'selection' is null or not an object"
I managed to track this error down to /fckeditor/editor/_source/internals/fckdialog.js line 112.
I don't understand in internal workings of FCKEditor fully. I have managed to work out that it's due to it trying to access the Editor which isn't about while in source view.
Adding a check for the EditMode and using the EditingArea.Textarea to select the selection seems to fix the problem. I'm not 100% sure this is the correct fix so an FCKEditor core dev will have to read though the patch I've attached.