出现Object reference not set to an instance of an object. 弄了半天没弄好。

加载页面的时候出现一行“Object reference not set to an instance of an object. ”我弄了半天没有弄好。页面代码：<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="lx.aspx.cs" Inherits="RedDoo.admin.yp.lx" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>Untitled Page</title>
    <link href="../admincss.css" rel="stylesheet" type="text/css" />
</head>
<body>
    <form id="form1" runat="server">
        <div>
         <table width="500" border="1" align="center" cellpadding="0" cellspacing="0" bordercolorlight="#cccccc"
                bordercolordark="#FFFFFF" id="tab" runat="server">
                    <tr bgcolor="#efefef">
                        <td height="22" colspan="2">
                            &nbsp;会员类型管理 - <strong><%=_name %> </strong>
                        </td>
                    </tr>
                    <tr>
                        <td height="22" width="50%">
                            <asp:RadioButton ID="radvip3" runat="server" Text="试用申请中" GroupName="a1" /></td>
                        <td width="50%">
                            <asp:RadioButton ID="radvip4" runat="server" Text="试用会员" GroupName="a1" /></td>
                    </tr>
                    <tr>
                        <td height="22" width="50%">
                            <asp:RadioButton ID="radvip5" runat="server" Text="普通申请中" GroupName="a1" />
                            <font color="red">(等待收费)</font></td>
                        <td width="50%">
                            <asp:RadioButton ID="radvip6" runat="server" Text="普通会员" GroupName="a1" /><font color="red">(已收费)</font></td>
                    </tr>
                    <tr>
                        <td height="22" width="50%">
                            <asp:RadioButton ID="radvip1" runat="server" Text="VIP 申请中" GroupName="a1" />
                            <font color="red">(等待收费)</font></td>
                        <td width="50%">
                            <asp:RadioButton ID="radvip2" runat="server" Text="VIP 会员" GroupName="a1" />
                            <font color="red">(已收费)</font></td>
                    </tr>
                    <tr>
                        <td height="22" width="50%">
                            <asp:RadioButton ID="rdvip7" runat="server" Text="大卖场商家" GroupName="a1" />&nbsp;
                        </td>
                        <td width="50%">    归属于<asp:DropDownList ID="ddlbig" runat="server">
                            </asp:DropDownList>大卖场商家
                        </td>
                    </tr>
                    <tr>
                        <td height="22" colspan="2" align="center">
                            &nbsp;<asp:RadioButton ID="radkey1" runat="server" GroupName="u5" Text="正常" />
                            &nbsp;&nbsp;
                            <asp:RadioButton ID="radkey2" runat="server" GroupName="u5" Text="到期" />
                            &nbsp; &nbsp;<asp:RadioButton ID="radkey3" runat="server" GroupName="u5" Text="推荐" />&nbsp;
                            &nbsp;<asp:RadioButton ID="radkey" runat="server" GroupName="u5" Text="待审" /></td>
                    </tr>
                    <tr>
                        <td height="22" colspan="2" align="center">
                            <asp:CheckBox ID="chkre" runat="server" Text="重新计算时间" />&nbsp; (选择则该企业收费计算时间从现在开始)</td>
                    </tr>
                    <tr>
                        <td height="22" colspan="2" align="center">
                            重新设定会员开放天数<asp:TextBox ID="txtztian" runat="server" Width="50px"></asp:TextBox>(指从会员开始到结束的总天数，对各申请中会员无用)</td>
                    </tr>
                    <tr align="center">
                        <td height="22" colspan="2">
                            <asp:Button ID="btnok" runat="server" CssClass="input1" OnClick="btnok_Click" Text=" 提 交 " />
                            <asp:Button ID="changepass" runat="server" OnClick="changepass_Click" Text="恢复密码为 123" /></td>
                    </tr>
            </table>
        </div>
    </form>
</body>
</html>