How to disable background when jQuery Modal Dialog is opened with modal is false

Button is not trigerring when i use modal:true, without including it works fine but the background is also active when the popup raises.

<script type="text/javascript">
        $(function () {
            $("[id*=btnadd]").live("click", function () {
                
                $("#modal_dialog").dialog({

                    title: "Manage Branch",
                    autoopen: false,
                
                    width: 500,
                    buttons: {
                        ADD: function () {
                            var textvalue = $("#<%=TextBox2.ClientID%>").val();
                            $('#<%= hndtxt.ClientID %>').val(textvalue);
                            $('#<%=add.ClientID %>').click();
                        },
                        Close: function () {
                            $(this).dialog('close');
                        }
                    }
                });
            });
        });
</script>

<input type="button" id="btnadd" value="Add Branch" name="btnadd" style="float: right" />
      <asp:Button ID="add" runat="server" Text="ADD" Style="display: none" OnClick="btninsert_Click">
    </asp:Button>

<div id="modal_dialog" style="display: none">
           <div class="tab_container">
                <div id="tab2" class="tab_content">
                    <table cellspacing="0">
                        <tbody>
                            <tr>
                                <td>
              
                                                                          
                                     <b>Branch:
                                        <asp:TextBox ID="TextBox2" runat="server" Style="margin-left: 97px"></asp:TextBox>
                                         <asp:label id="lbl_status" runat="server"  cssclass="red" text=""></asp:label>
                                        
                                     <br />
                                        <br />
                                                  </td>
                            </tr>
                                                                  
                        </tbody>
                   
                    </table>
                         
                </div>
                <!-- end of #tab1 -->
            </div>
            <!-- ID -->     

                     
        </div>

 protected void btninsert_Click(object sender, EventArgs e)
        {
            ClientScript.RegisterStartupScript(Page.GetType(), "key", "alert('Button Clicked')", true);

        }