Error in supplier balance

Hi, Gurus

Please help us for the following issue

1 – We have a supplier number 3328.

2 – This supplier is a service supplier ( it means the invoices is entered without an POs ).

3 – This supplier has five invoices.

4 – All these invoices are paid.

5 – The Accounts Payable Negative Supplier Balance reports shows a balance for this supplier as attached file.

6 – The Accounts Payable Negative Supplier Balance reports shows the right data for all suppliers except this one.

We think there is an error concerning supplier invoices or checks, So Why the Accounts Payable Negative Supplier Balance report shows a data for this supplier ?.

Please provide solutions as soon as possible.