Looking for some advice. I am getting the following error when trying to join reports in a table view

I am trying to Add "DueDate" from the Table "Eagle _Network_DueDates" to a pivot table primarily built on  a table titled "Eagle_All_Hours_Report" by joining the "Network" columns using the table lookup function

Below is the relationship. 

I'm just looking for clarification why this join isn't working in the pivot table? What do I need to do to make it work?

Thanks