This error occurs with some Shape5 templates (as well as others such as Youjoomla). The reason this is happening is because there is a constant called "TEMPLATEPATH" that Wordpress uses throughout that these Joomla templates are also using. We cannot change the name of the constant in Wordpress because we would lose support for Wordpress plugins and themes.
However, we CAN change it in the Joomla template. Open up all of the PHP files in the directory where your Joomla template is ([Your Joomla site]/templates/[name of your template]/) and look for TEMPLATEPATH and rename it to something like S5_TEMPLATEPATH. Frequently, the only file you will have to change is index.php.
I know there's at least one of them on line 69 of /users/caffeine/public_html/templates/pantheon/index.php and I suspect it gets defined somewhere near the top of that index.php file.
Kindest regards,