Employees with Sal Sac

Since the update to STP2, I am getting an error msg "GrossAmount Error: The derived aggregated gross YTD amount must not be a negative amount (ATO Error CMN.ATO.PAYEVNTEMP.000389)" for my employees that have salary Sacrifice when using the desktop interface to process. It won't go through. The salary sac amount has always been keyed as a negative to reduce the Net Payment accordingly. If I change it to a positive, it adds the amount to the Net Pay. However, if I use the Web Broswer it deducts the amount even though the entered amount is a positive. This is an online file, how is it doing the same step different ways?