Error (when notifuing user about comments posted?)

Greetings,

I have installed Drupal 4.7.2 and after I post a comment to a forum thread the following message appears:

user warning: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1 query: SELECT u.mail, u.name FROM users u LEFT JOIN users_roles ur on u.uid = ur.uid WHERE in /home/user/public_html/includes/database.mysql.inc on line 120.

This happens when user uses email notification (about new comments posted).

Can someone tell me how to handle this?

PHP 4.4.2, MySQL 4.1.18

All the best,

Konstantin