Can't pay balance of order with reward points

I use Nop1.6 and VS 2008 (don't have new VS yet so can't upgrade)

My customer has enough reward points to pay the balance of the order.
I use one page checkout
on checkoutonepage.aspx - paymentMethod, customer checks:  use reward points and doesn't select a payment method since payment method is not required (has enough reward points to pay everything)
Customer can't move from screen since page is expecting a payment method.