PHP error: Failed opening '' for inclusion (include_path='.:/usr/share/php')

Hi all, maybe you can help me, as I can't find a solution on google or php-related sites... I get the following error when trying to render a PHP page: ---* Warning*: Failed opening '' for inclusion (include_path='.:/usr/share/php') in */home/mmielke/public_html/helpdesk/index.php* on line *4 *--- Any clues? Martin