User Warning error message

Hello,

I need help with a strange issue I started to experience.
Out of the blue, both of my Drupal installations started giving me the followoing error message on their homepages:
user warning: %s in /web/includes/database.mysql.inc on line 172.
Here is that line: trigger_error(check_plain(mysql_error($active_db) ."\nquery: ". $query), E_USER_WARNING);

This happens intermittently.Both databases have not been touched in a while and the host claims there is nothing wrong on their end.
No modules have been installed in quite a while either.

Thank you for your help,
isp