try changing line 935 to:
if (($WA_Store_Cart->TotalColumn("TotalPrice") != 0) && (WA_eCart_FormatNumber($WA_Store_Cart->DisplayInfo("Price") - (($WA_Store_Cart->DisplayInfo("Price")/$WA_Store_Cart->TotalColumn("TotalPrice")) * $WA_Store_Cart->GetDiscounts()), false, 2) > 0)) {