I just tried to connect two tables without primary keys, and got your error message, the relationship was indeterminate. After I changed a field to be the primary key in the parent database, the relationship now said one-to-many and I could try to enforce referential integrity.
To sum up: Your Contacts table is the child table, tied to the Projects table which is the parent table. This is a one-to-many relationship. The primary key for the Contacts table is Cntct#. Then, in the projects table, I would store the Cntct#. And in Tools, Relationships they can be connected.
If you have this set already, then I don't know why you are getting the error message. If this is not your join, then post back and hopefully someone will help you.