567749 Smarty Error on Joomla CiviCRM Installation

We're using Joomla Version 1.5.15 and CiviCRM 3.3 extension, and suddenly when we go to backend we get the following error (with errors enabled): Fatal error: Call to undefined function smarty_core_load_plugins() in /var/www/USER/data/www/[login to view URL]%%9D/9D3/9D3B6E05%%[login to view URL] on line 4 We've tried deleting templates_c folder, etc... no luck. Frontend Civi pages give a server error. We've made no major changes to the site, but I think it could be related to the server, which we have root access to.