I managed to achieve my goal in a round-about way. I have a combobox that pulls records from the Contacts table and saves the ID to a new cell I created on the Materials database. I labled that cell CheckoutID. I then joined CheckoutID on the Materials table to ID of the Contacts table using the relationships page.
Then I was able to create a subform with the Master field linked to the CheckoutID I created. The Child field is linked to the ID of the contacts table. Then the only thing left was to have the subform update whenever a new contact was selected form the combobox. So I edited the properties of that combobox, slected Event - On Change and added the following code
Code:
[Contact subform].Requery
I tried to upload the database but I cannot get the filesize under 500kb :/
Here's a screenshot to give you an idea of what I did.