Issue with dropdown area

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ASP.NET

Hi everyone.. I am not getting pincodes and std codes if i use updatepanel inside dropdown for area.. How to solve this. My design and code. i m getting desired output if i dont use updatepanel.

<tr>
<td>
Area<span class="mandatory">*</span>
</td>
<td>
<asp:UpdatePanel ID="UpdatePanel4" runat="server">
<ContentTemplate>
<asp:DropDownList class="w216 dpreq" ID="dparea" runat="server" style="height:25px;"
AppendDataBoundItems="true" AutoPostBack="True" OnSelectedIndexChanged="dparea_SelectedIndexChanged">
</asp:DropDownList>
</ContentTemplate>

<Triggers>
<asp:AsyncPostBackTrigger ControlID="dparea" />
</Triggers>
</asp:UpdatePanel>
</td>

</tr>

protected void dparea_SelectedIndexChanged(object sender, EventArgs e)
{
if (dparea.SelectedIndex != 0)
{
SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["Constr"].ConnectionString);
con.Open();
SqlDataAdapter adp = new SqlDataAdapter("SELECT [Pincode],stdcode FROM [viewarea] WHERE ([AreaID] = " + dparea.SelectedValue.ToString() + ")", con);
DataTable tab = new DataTable();
adp.Fill(tab);
string pincode = tab.Rows[0][0].ToString();
string stdcode = tab.Rows[0][1].ToString();
txtpinno.Text = pincode;
txtstdcode.Text = stdcode;
con.Close();
}
}