下传组件老说PostedFile = null

上传组件老说PostedFile = null
测试时，上传组件传图片。代码如下，但传不上去 测试PostedFile = null
我用好几个上传代码，最后都穿不上去，就是  postefile =null 

到底有没有高手能解决啊，。。！！！！！

 <asp:Panel ID="MyPanel2" runat="server" >
               <tr>
                <td>
                    上传照片：</td>
                <td colspan="3" s="">
                    <asp:FileUpload ID="FileUpload1" runat="server" />
                    <asp:Button ID="button1" runat="server" Text="上　传" CssClass="BnCss" OnClick="button2_Click" />
                    <asp:Label ID="Label6" runat="server"></asp:Label></td>
            </tr>
            
            </asp:Panel>  



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 protected void button2_Click(object sender, EventArgs e)
    {
        if (FileUpload1.PostedFile.ContentLength == 0)
        {
            src = "";
        }
        else
        {
            string zname = this.B_TITLE.Text.Trim();
            string strFilePath = FileUpload1.PostedFile.FileName;
            FileInfo fl = new FileInfo(strFilePath);
            string Ext = fl.Extension;
            if (Ext.Equals(".jpg") || Ext.Equals(".gif") || Ext.Equals(".png") || Ext.Equals(".ico"))
            {

                src = zname + Ext;

                string ServerPath = Server.MapPath("~");
                string strSeraPath = ServerPath + "\\picture\\" + src;
                FileUpload1.PostedFile.SaveAs(strSeraPath);
                this.Label1.Text = "图片上传成功";
                src = zname + Ext;