Keeping track of payments

You guys helped me with this sheet a while ago


http://www.excelforum.com/excel-gene...-payments.html

but i have got a bit of an error in it so im hoping you could help a bit more

on the payments sheet, balance column it is only referencing to col b but it needs to ref to col a & b otherwise it is giving a false balance for the plot numbers if you understand any of that
i would appreciate it if you could have a look for me