[Lynne]

If you are positive all your templates have been properly upgraded (that means either reverting it or doing a Compare between your version and the default Jelsoft one for every single template in red and for every single non-Jelsoft template(modifications)), then try disabling your plugins and then see if you still get the error.
Note: To temporarily disable the plugin system, edit config.php and add this line right under <?php

PHP Code:

define('DISABLE_HOOKS', true);