Thread:Extension talk:ParserFunctions/Not working: Making wiki go blank with error message

After download and placing the extension in the extensions folder and adding:

require_once( "/wiki/extensions/ParserFunctions/ParserFunctions.php" );

to the localsetttings.php page the website loads with:

Warning: require_once(/wiki/extensions/ParserFunctions/ParserFunctions.php): failed to open stream: No such file or directory in /home/pktweb/www/wiki/LocalSettings.php on line 145

Fatal error: require_once: Failed opening required '/wiki/extensions/ParserFunctions/ParserFunctions.php' (include_path='.:/usr/share/pear:/usr/share/php') in /home/pktweb/www/wiki/LocalSettings.php on line 145

Does anyone know how to fix this?