2 Chart on the same page

Please i'm using 2 dropdownlist to show to different record but i can't put the two chart on a single page at the same time
why?
here are the code
Select Auction:<asp:DropDownList ID="DropDownList1" runat="server" onselectedindexchanged="DropDownList1_SelectedIndexChanged" AutoPostBack = "true"> </asp:DropDownList>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Select Auction:&nbsp;&nbsp;&nbsp; <asp:DropDownList ID="DropDownList2" runat="server" onselectedindexchanged="DropDownList2_SelectedI ...