Logs: Cannot modify header information

In the Logs I find:

Cannot modify header information - headers already sent by (output started at /var/www/mydomain/drupal-5.1/modules/community_tags/community_tags.module:424) in /var/www/mydomain/drupal-5.1/includes/common.inc on line 141.

The tagging however seems to work. (or creates nasty side effects in case of image nodes as described in http://drupal.org/node/159479)