When theme() is called from within a shutdown function, such as within syslog_watchdog, if the theme registry has been cleared, the following error will be generated:
PHP Fatal error: require_once() [function.require]: Failed opening required './sites/all/modules/contrib/cck/theme/theme.inc' (include_path='.:/usr/share/php:/usr/share/pear') in /var/www/sites/all/modules/contrib/cck/content.module on line 176
This occurs because the current directory is no longer the Drupal root directory and the include occurs via a relative path. The patch below modifies content.inc to use module_load_include() instead of require_once. This, in conjunction with the DRUPAL_ROOT backport for D6 (http://drupal.org/node/1345402) solves this fatal error by including the file using an absolute path.