Foreign Key crashes Datadeploy problem

System

Does this problem sound familier to anyone ?

We hav a database which has several tables that contain two foreign keys used for a many to many mapping e.g DocumentID and LinkID maps links and Documents to each other.
The problem is, if I don't make these explicitly foreign keys in the database then when I run iwsyncdb.ipl it complains of the lack of foreign keys.
If I add these foriegn keys explicitly in the DB and then use the DD admin to regenerate the dbschema files it crashes with a ddui error and I have to reboot the machine.

Must I add the foreign keys and then change the dbschemas by hand ?

cheers

/Nick