Trouble with including related values.

I am implementing a inventory system, and am a little stuck with one of my value lists. I have the following relationships set:

I have it set so the user can enters Prime Contract numbers. Next they can select a Prime Contract number and then enter a Subcontract number. And finally they can select the Prime Contract number, be shown a list of related Subcontracts and finally enter Task Orders. This all works fine.

For my Inventory Items database I have it working where the user can select a Prime Contract for the item. Then they can select a Subcontract based on the Prime Contract. So far this all works.

What I would like is based on the Subcontract for the user to be able to select multiple Task Orders. This is where I run into trouble. If I setup the value list to show all Task Orders, I can select a Task Order, and the records are created through the portal. However if I choose "Include only related values starting from:" I get <no values defined> in my Pop-up menu.

I've included the Value List below:

Any help would be appreciated.