56758 Debug/Recompile frontend

I have a customer that's come to me with a "Runtime-error '6': Overflow" in his order entry system. From what I've discovered, there is a frontend form that is computing a value that doesn't fit into the data type of the field. Googling the problem leads me to think that the front end needs to be recompiled or recoded. If you know how to fix this please give me your best price to fix. Thanks South O Design