GridView radio button problem !!!!

[Shantanu88d]

Hi,
I have added a template field on my grid view and added radio buttons to it. I have also given them group name. However when grid view populates, radio buttons behave like check boxes and multiple of them are getting selected.
Here's code for GridView for ur reference.
Plz help

<asp:GridView ID="GridView1" runat="server" CellPadding="4" DataSourceID="SqlDataSource2"
                            ForeColor="#333333" GridLines="None" AllowPaging="True" Style="text-align: left"
                            Width="462px">
                            <AlternatingRowStyle BackColor="White" />
                            <Columns>
                                <asp:TemplateField HeaderText="*">
                                    <ItemTemplate>
                                        <asp:RadioButton ID="radio1" runat="server" GroupName="grp1" />
                                    </ItemTemplate>
                                </asp:TemplateField>
                            </Columns>
                            <EditRowStyle BackColor="#2461BF" />
                            <FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
                            <HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
                            <PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" />
                            <RowStyle BackColor="#EFF3FB" />
                            <SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
                        </asp:GridView>