On deleting a task the following error happend:
ZfExtended_Log on www.translate5.net - Kurzmeldung: exception 'PDOException' with message 'SQLSTATE[23000]: Integrity constraint violation: 1451 Cannot delete or update a parent row: a foreign key constraint fails (`translate5Net`.`LEK_terms`, CONSTRAINT `fk_LEK_terms_2` FOREIGN KEY (`collectionId`) REFERENCES `LEK_languageresources` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION)'

The problem is the above listed foreign key which is configured with "NO ACTION". That leads to the foreign key constraint on task deletion.

Fix: change the foreign key.