<asp:DropDownList ID="ddlSource" runat="server" DataSourceID="SqlDataSource1" DataTextField="vcSuplierNm" ViewStateMode="Enabled DataValueField="vcSuplierCode" EnableViewState="true" AppendDataBoundItems="true" OnSelectedIndexChanged="ddl_OnSelectedIndexChanged" AutoPostBack="true"></asp:DropDownList>
Add property ViewStateMode="Enabled" and EnableViewState="true"
in drop DropDownList
Add property ViewStateMode="Enabled" and EnableViewState="true"
in drop DropDownList