All the above didnt work for me.
The solution here was to edit the following file (after updating tinyMCE to modx_tinymce_3241 on MODX 1.0.6)
Edit the following file:
/manager/media/browser/mcpuk/seturl_js_tinymce.inc
Change from:
<script language="javascript" type="text/javascript" src="[+editor_path+]jscripts/tiny_mce/tiny_mce_popup.js"></script>
<script language="javascript" type="text/javascript" src="[+editor_path+]tinymce.modxfb.js"></script>
To:
<script language="javascript" type="text/javascript" src="[+editor_path+]/jscripts/tiny_mce/tiny_mce_popup.js"></script>
<script language="javascript" type="text/javascript" src="[+editor_path+]/tinymce.modxfb.js"></script>
(Note the / behind [+editor_path+])
