mysql_affected_rows error

Warning: mysql_affected_rows(): A link to the server could not be established in /var/www/vhosts/blog.eyetag.de/httpdocs/wp-includes/wp-db.php on line 159

… this is what my wp 2.0 says to me. i deleted some tables, but none of the wp_ prefix. please, anyone? looks like a nasty error!

thanks!
et