Duplicate entry into the activity_targets table

Hey guys, long time no bug! For some reason I've recently began to receive these error messages:

User warning: Duplicate entry '602-0-en' for key 1 query: INSERT INTO activity_targets (aid, uid, amid, language) VALUES (602, 0, 1234, 'en') in _db_query() (line 141 of /var/drupal/includes/database.mysql.inc).

When looking into the activites_targets table, I see old amid's being assigned to new aid's. (i.e. very old messages are being assigned to new activities).