.Net Framework Version issue

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C#

ASP.NET

In GridView i've the following DropDownlist Control. When I click on some index then SelectedIndexChanged event is firing in .Net Framework 2.0 version of Windows Vista and is working fine. Also When im using .Net Framework 4.0 in windows 8 version working fine.
But the issue is when im using .Net Framework 2.0 in windows 8 version page is getting refresh rather it has to fire dropdownlist selectedindexchanged event..

<asp:TemplateField>
	<ItemTemplate>
       <asp:DropDownList ID="ddlCLStatus" runat="server" AutoPostBack="true" CssClass="ddlblack" CausesValidation="false"
        OnSelectedIndexChanged="ddlCLStatus_SelectedIndexChanged" SelectedValue='<%# Bind("Status") %>'>
            <asp:ListItem Text="Pending" Value="P"></asp:ListItem>
            <asp:ListItem Text="Cleared" Value="C"></asp:ListItem>
            <asp:ListItem Text="Returned" Value="R"></asp:ListItem>
            <asp:ListItem Text="Clear All" Value="CA"></asp:ListItem>
            <asp:ListItem Text="Returned All" Value="RL"></asp:ListItem> <%--Added by Gaurav Sikarwar on 02-03-2015--%>
        </asp:DropDownList>
	</ItemTemplate>
</asp:TemplateField>