FIXED: Fatal error in ../modplugin/1.include.cache.php on line 34

Fatal error: Call to undefined method modX::isFrontend() in /var/www/site.com/public_html/core/cache/includes/elements/modplugin/1.include.cache.php on line 34

I am getting this error when I am trying to edit a page. I just upgraded from 2.0.8, where I recieved two warnings as posted in another thread. I have flushed the cache and sessions to see if this helped.

Furthermore, the system settings and package management pages are blank (the top and left navigation panels are there, but nothing on the main panel). But this is only in Firefox 5.0. It works in IE.

Modx Revo 2.1.2 Traditional
Server: Linux 2.6.18-338.5.1.el5.lve0.8.25 #1 SMP Mon Mar 28 12:25:47 EEST 2011 x86_64
PHP Version is 5.3.3
MySQL is 5.1.48 (client)
pdo_mysql: PDO Driver for MySQL

1. That method is deprecated: http://rtfm.modx.com/display/revolution20/Summary+of+Legacy+Code+Removed+in+2.1 - you probably should have deactivated it before upgrading.
2. Empty the core/cache/ directory.
3. Find the plugin with ID 1 in your database table ’modx_site_plugins’, and set the ’disabled’ field to 1.
4. Reload the manager page.

Hmm. It was an old version of TinyMCE (4.01). I upgraded to newest version and it is working now. Thanks.