There should be another message in your console displaying the SQL exception that occurs.
I recently stumbled into this after renaming entity A and creating entity B using entity A’s old name and using the same associations. What happened in my case is that the modeler created unique constraints for the database based on the creation of the new entity. But because the newly created entity name was exactly the same as the old one, the exact same constraints already existed, causing an SQL exception and DDL error.
So basically, you need to find the SQL exception so you know what DDL command is causing the error. You could also find the DDL commands from the window you see whenever the modeler is trying to synchronize the database.
Any update on this? Did anyone get any answers?