I got the same problem. I got that message to go away by commenting that code out in the ~/fckeditor/editor/js/fckeditorcode_ie.js file:
GetParentForm:function(){/*return this.LinkedField.form;*/}
However, the issue about commenting this out is that fckEditor1.Value loses the HTML tags. VWG release 6.2.2a for what I need to do. The FCKEditor version that I'm using is 2.6.3 (latest current). Anybody got a fix or workaround?