Payment term not functioning

Hi gurus

We have 2%10 payment term defined as 2% in paid in 10 days and 0 % for 30 days.

I have posted an FB60 invoice with pmt term as 2%10, (posting and doc date as) 5/15/2009 and tried to pay on 5/22/2009 via payment program, which is within 10 days to take advantage of 2% discount from vendor.

But on F110 screen this invoice is not being poicked up by the payment program with next payment date 5/25/2009.

But, when I tried running the payment program with "next payment run" as 6/25/2009, it is then being picked up, but we are losing the cash discount.

PLease advise , what should I do to take the 2% discount

Many thanks in advance

MSJ