AP aging report returns all zeros

Can anyone enlighten me as to why our vendor aging reports are returning all of our vendors with a zero balance? When I look at the Aging period definition statistics for a particuar vendor, I see a negative amount under Open invoices, and a $0.00 amount under Open payments. Is the aging report driven from the open payments field? And is that why it is generating with all zero balances?

If that is the cause, how does the Open payments amount become an amount other than $0.00? I’m trying to understand some basic accounting logic here. Any explanation regarding these issues would be appreciated!