Did you enter a bill and then enter a check to pay the bill? The bill will still show as unpaid because it is not "linked" to the check.
To correct this payment:
1. Go to the check written to pay the bill and double click to open it
2. Enter Accounts payable in the Expense Account drop down list on the lower portion of the check
3. Go to Vendor>Pay bills>click on the bill
4. Click "Set credits" in the area below the list of bills
5. Set the correct date and choose "Pay Selected Bills"
This will link the payment to the bill