AutoPostBack is Not Working On page

Hello ,
I have a dropdown list on page and place AutoPostBack="True" .
and  have some code in select change index but postback is not working.
the code for dropdown here:-

<asp:DropDownList ID="ddlindustry" runat="server" CssClass="dropdown" Width="200px" onselectedindexchanged="ddlindustry_SelectedIndexChanged" AutoPostBack="true"> <asp:ListItem Value="0"> --------- Industry Type---------</asp:ListItem> <asp:ListItem>Accounting </asp:ListItem> <asp:ListItem>Advertising </asp:ListItem> <asp:ListItem>Agriculture </asp:ListItem> <asp:ListItem>Animation </asp:ListItem> <asp:ListItem>Architecture </as ...