-7040: Referential constraint not allowed 

Explanation:

There is already a referential CONSTRAINT definition with the specified referencing table. Moreover, CASCADE dependency arises. Under these conditions, all CONSTRAINT definitions with the indicated referencing table must specify either CASCADE or RESTRICT.

User Action:

Rethink the desired effect, because it would result in basically contesting situations. You can view information about existing referential CONSTRAINT definitions using a QUERY statement issued on the DOMAIN.FOREIGNKEYCOLUMNS system table.