Sheena,

The message has absolutely nothing to do with the database at all. The message is saying that a relation existed in the runtime environment and it has been broken. This occurs if you change the order on the child table for example.

USE Parent
USE Child ORDER SomeTag IN 0
SET RELATION TO SomeExpression INTO Child

SELECT Child
SET ORDER TO AnotherTag && Relation is broken

Check for anything changing the controlling tag on a table. Also, closing the child table will result in the same message.