Payment not applied to current invoice

Hi,

I have Sage Timeslips 2013.  I am running bills for this month, and a client's balance does not reflect a payment that was made and applied to a bill, two cycles ago.  That bill was approved, and the payment shows with the yellow envelope in A/R transactions, that it was on an approved bill.  It was reflected on the last bill, but not on this one.

Help!

Thanks