Paid/Credit on Invoice does not agree.

Hi,

My client is using SAP 2005 SP 1 Patch 42.

He has an invoice $85000.

Incoming payment against this invoice is $25000 and $20000.

The Balance of this invoice should be $40,000.

However, when I go to the invoice, Paid/Credit = $85000 and the Balance due = 0.

I have checked there is no Credit Note raised against this invoice.

Any suggestion on how I can find out what is going on?

Thanks in advance for your help.