the onchange code is not correct
onChange="onChange="document.InsoleCart_1_ATC_0.<Size>.value = "
should be:
onChange="document.InsoleCart_1_ATC_0.InsoleCart_1_Size_Add.value = document.InsoleCart_1_ATC_0.InsoleCart_1_Price_Add[document.InsoleCart_1_ATC_0.InsoleCart_1_Price_Add.selectedIndex].text"