无法更新SQL服务器中的varbinary(max)列

我正在尝试使用varbinary (SQL Server 2008)更新我的个人资料图片。它似乎没有更新我放在文件上传的图片。然后我尝试将我的个人资料图片列设置为NULL，它似乎也不起作用。下面是我用来将我的个人资料图片列更新为NULL的代码，并使用fileupload更新个人资料图片并将其转换为varbinary(MAX)。请帮我看看我做错了什么。谢谢!

    protected void btnUpload_Click(object sender, EventArgs e)
    {
        String username = (String)Session["username"];
        string filePath = FileUpload1.PostedFile.FileName;
        string filename = Path.GetFileName(filePath);
        string ext = Path.GetExtension(filename);
        string contenttype = String.Empty;
        switch (ext)
        {
            case ".jpg":
                contenttype = "image/jpg";
                break;
        }
        if (contenttype != String.Empty)
        {
            Stream fs = FileUpload1.PostedFile.InputStream;
            BinaryReader br = new BinaryReader(fs);
            Byte[] bytes = br.ReadBytes((Int32)fs.Length);
            string strQuery = "Update LoginRegisterOthers Set profilepic = NULL Where username = '" + username + "'";
            SqlCommand cmd = new SqlCommand(strQuery);
            InsertUpdateData(cmd);
            //insert the file into database
            //string strQuery2 = "Update LoginRegisterOthers Set profilepic = @Data Where username = @Username";
            //SqlCommand cmd2 = new SqlCommand(strQuery2);
            //cmd2.Parameters.Add("@Data", SqlDbType.Binary).Value = bytes;
            //cmd2.Parameters.Add("@Username", SqlDbType.VarChar).Value = username;
            //InsertUpdateData(cmd2);
            //lblUpload.ForeColor = System.Drawing.Color.Green;
            //lblUpload.Text = "Profile Updated.";
            Response.Redirect("MemberProfile.aspx");
        }
        else if (contenttype == String.Empty)
        {
            lblUpload.Text = "Please select your image before uploading!";
        }
        else
        {
            lblUpload.ForeColor = System.Drawing.Color.Red;
            lblUpload.Text = "File format not recognised." + " Upload Image formats";
        }
    }
    private Boolean InsertUpdateData(SqlCommand cmd)
    {
        SqlConnection con = new SqlConnection("Data Source=localhost; Initial Catalog=project; Integrated Security=True");
        cmd.CommandType = CommandType.Text;
        cmd.Connection = con;
        try
        {
            con.Open();
            cmd.ExecuteNonQuery();
            return true;
        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
            return false;
        }
        finally
        {
            con.Close();
            con.Dispose();
        }
    }