Warning: require_once(DIR/includes/functions_log_error.php) [function.require-once]: failed to open stream: No such file or directory in ./includes/class_core.php on line 3281

Fatal error: require_once() [function.require]: Failed opening required 'DIR/includes/functions_log_error.php' (include_path='.:/usr/local/share/pear') in ./includes/class_core.php on line 3281

I'm getting this error whenever I try to surf around the forums, after a few tries it allows me to surf then shows this again every now and then.