TPC cannot be added after assigning/post a Third Party Contract(TPC) to a student

On page Student Financials>> Payment Plans>> Third Party Contracts>> Assign, I can assign/post the third party contract to some students successfully. But for some other students, there is no error after assign/post. However the item is not listed on page Student Financials>> View Customer Accounts --> Payment Plans.

I checked Tree manager and Third Party Contract (TPC) definition. Cannot find anything wrong. The TPC has eligible Nodes TUITION. I assume the TPC setup and tree manager should be correct since I can add some students successfully. I just cannot find out why it is working for some students, but not working for others? Did anyone see this kind problem before? Please help!