I think it is since WordPress 3.0 that this issue occurs:
The additional "Insert Table" button from TinyMCE doesn't work. Clicking the button results in a empty popup.
We added the button via several plugins (TinyMCE Advanced, WP Super edit), but they all have the same problem.
A error in line 10 of "form_utils.js" is causing this
var themeBaseURL = tinyMCEPopup.editor.baseURI.toAbsolute('themes/' + tinyMCEPopup.getParam("theme"));
We 'fixed' this by commenting out this line in the plugin's file, but I don't think that's the best way to go.
Anybody else having the same issue?