Grid view Row Index Problem

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
        BackColor="White" BorderColor="#CCCCCC" BorderStyle="None" BorderWidth="1px"
        CellPadding="3" Width="900px" ShowFooter="True" DataKeyNames="UQD_ID">
        <Columns>
        <asp:BoundField HeaderText="Subject" DataField="UQD_Subject" />
        <asp:BoundField HeaderText="Query" DataField="UQD_Description" />
        <asp:BoundField HeaderText="Query Date" DataField="UQD_InsertDate" />
        <asp:TemplateField HeaderText="Reply">
        <ItemTemplate>
            <asp:TextBox ID="txtReply" runat="server"></asp:TextBox>
        </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="Is Reply">
        <ItemTemplate>
            <asp:CheckBox ID="chk" runat="server" />
        </ItemTemplate>
        <FooterTemplate>
            <asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" />
        </FooterTemplate>
        </asp:TemplateField>
        </Columns>
        <FooterStyle BackColor="White" ForeColor="#000066" />
        <HeaderStyle BackColor="#006699" Font-Bold="True" ForeColor="White" />
        <PagerStyle BackColor="White" ForeColor="#000066" HorizontalAlign="Left" />
        <RowStyle ForeColor="#000066" />
        <SelectedRowStyle BackColor="#669999" Font-Bold="True" ForeColor="White" />
        <SortedAscendingCellStyle BackColor="#F1F1F1" />
        <SortedAscendingHeaderStyle BackColor="#007DBB" />
        <SortedDescendingCellStyle BackColor="#CAC9C9" />
        <SortedDescendingHeaderStyle BackColor="#00547E" />
    </asp:GridView>

public partial class AdminReply : System.Web.UI.Page
{
    string con = ConfigurationManager.ConnectionStrings["conn"].ConnectionString;
    DataSet ds = new DataSet();
    SqlParameter[] param;
    protected void Page_Load(object sender, EventArgs e)
    {
        if(!IsPostBack)
        {
            BindGrid();
        }
    }

   
    private void BindGrid()
    {
        ds = SqlHelper.ExecuteDataset(con, CommandType.StoredProcedure, "UQAdminView");
        GridView1.DataSource=ds;
        GridView1.DataBind();
    }
    protected void btnSubmit_Click(object sender, EventArgs e)
    {
        int UQD_ID;
        foreach (GridViewRow Row in GridView1.Rows)
        {
            if (((CheckBox)Row.FindControl("chk")).Checked)
            {
             
                UQD_ID = Convert.ToInt32(GridView1.DataKeys[Row.RowIndex].Values);

                bool IsReply = ((CheckBox)Row.FindControl("chk")).Checked;

                string Reply = ((TextBox)Row.FindControl("txtReply")).Text;

                param = new SqlParameter[3];
                param[0] = new SqlParameter("@UQD_ReplyDescription", Reply);
                param[1] = new SqlParameter("@UQD_IsReply", IsReply);
                param[2] = new SqlParameter("@UQD_ID", UQD_ID);

                SqlHelper.ExecuteNonQuery(con, CommandType.StoredProcedure, "UQAdminUpdateReply", param);


            }
        }
    }
}