在c# asp.net中上传图像时，FileUpload没有文件

FileUpload在ASP中上传图像时显示空文件。净c#。我的页面连接到一个母版页，所以当我点击上传按钮FileUpload控件显示空文件，但当我使用它没有母版页文件上传成功，请告诉我如何缩短这个问题。我正在使用这个代码。

<table>
        <tr>
    <td>Enrollment Id</td>
    <td>:</td>
    <td>
        <asp:TextBox ID="txtEnrollmentNo" runat="server" CssClass="text" AutoPostBack="true" OnTextChanged="txtEnrollmentNo_TextChanged"></asp:TextBox>
    </td>
    <td></td>
    </tr>
    <tr>
    <td colspan="4" style="font-weight:bold; text-align:center;">
    Student Details
    </td>
    </tr>
    <tr>
    <td colspan="3" style="background-color:#eee; padding:5px;">
    Upload Photo
    </td>
    </tr>
    <tr>
    <td colspan="3">
        <asp:Image ID="imgPhoto" runat="server" CssClass="imageUpload" />
    </td>
    <td></td>
    </tr>
    <tr>
    <td colspan="3">
        <asp:FileUpload ID="fileUploadPhoto" runat="server" onchange="readPhotoURL(this)" />
         </td>
    <td></td>
    </tr>
    </table>
    <div class="commonArea">
        <asp:Button ID="btnSubmit" runat="server" Text="Upload & Save" TabIndex="3"  onclick="btnSubmit_Click" />
    </div>

使用

的代码

protected void btnSubmit_Click(object sender, EventArgs e)
    {
        try
        {
            string extension = Path.GetExtension(fileUploadPhoto.PostedFile.FileName);
            fileUploadPhoto.PostedFile.SaveAs(Server.MapPath("~/StudentImages/Photo/") + txtEnrollmentNo.Text + extension);
            MessageBox("success", txtEnrollmentNo.Text); 
        }
        catch (Exception ex)
        {
            MessageBox("error",ex.Message);
        }
    }