I recently stumbled across an issue after an end-user was having a problem with Joomla! and logged in to edit some content items.
TinyMCE would show up fine as their editor but anytime that they would try to open the related pages within the editor including help, they would receive an blank page with a javascript error and an unparsed javascript string in the title such as these with their corresponding pages:
{$lang_about_title} - Help
{$lang_insert_image_title} - Insert/Edit image
{$lang_theme_code_title} - Edit HTML Source
{$lang_emotions_title} - Emoticons menu
The official error that Firefox was giving me is as follows:
uncaught exception: Permission denied to get property Window.tinyMCE
[Break on this error] undefined
tinyMCE has no properties
[Break on this error] var themeBaseURL = tinyMCE.baseURL + '/themes/' + tinyMCE.getParam("theme");
form_utils.js (line 10)
tinyMCE has no properties
[Break on this error] tinyMCE.setWindowArg('mce_windowresize', false);
functions.js (line 8)
tinyMCE has no properties
The problem was that the "Live Site" in the Global Configuration was set to (for example) "http://www.theclevergeek.com", while the user was entering "http://theclevergeek.com", omitting the www. and thus trying to execute Javascript from another domain. Though I didn't check, I suspect that JCE would still have the same problem because it is heavily based on TinyMCE as well.
This can simply be fixed by:
1) Entering the URL of the "Live Site" every time.
2) Fixing the Live Site parameter to meet your preferences.
3) Modifying your .htaccess file to forward everyone from http://www.theclevergeek.com to http://theclevergeek.com or visa versa.
A man goes to his doctor and says 'Hey, Doc, it hurts when I do this.' So the doctor says, 'Then stop doing that!'"