Invalid Join error is issued in the following situations:
Cannot use the <entity> entity twice in the same join condition. Change the join condition to use another entity
The same entity cannot be use in the same join condition.
Edit the join condition to use two different entities.
<Structure> cannot be used in a join condition since it is a Structure
Cannot use a structure in a join condition.
Remove the structure from your join condition.
Double-click on the error line to take you directly to the source of the error.