ASP.NET 在线图书销售系统，上架图书上传“时间”代码出错，望大神指正！！！

public partial class admin_addproduvts : System.Web.UI.Page
{
    public string FileNamePic;
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string filename = "pic" + System.DateTime.Now.ToString("YYYYMMDDHHmmssff");
        Boolean FileOK = false;
        string path = Server.MapPath("~/picture/");

        if (FileUpload1.HasFile)
        {
            string fileExtension = (FileUpload1.FileName).ToLower();
            string[] allowedExtensions = { ".gif", ".png", ".jpeg", ".jpg" };
            for (int i = 0; i < allowedExtensions.Length; i++)
            {
                if (fileExtension == allowedExtensions[i])
                { FileOK = true; break; }
            }
            if (FileOK)
            {
                try
                {

                    FileUpload1.PostedFile.SaveAs(path + filename + fileExtension);
                    Session["FileNamePic"] = filename + fileExtension;
                    Label1.Text = "文件上传成功！";
                }
                catch (Exception ex)
                { Label1.Text = "文件未上传！"; }
            }
        }
        else { Label1.Text = "文件不是图片类型"; }
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
      
    }
    protected void Button3_Click(object sender, EventArgs e)
    {
        SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ShoppingWebDBConnectionString"].ConnectionString);

        conn.Open();
        string sql = "insert into Products(Name,Picture)values(@Name,@Picture)";
        SqlCommand cmd1=new SqlCommand(sql,conn);
        
        cmd1.Parameters.Add(new SqlParameter("@Name", SqlDbType.VarChar, 100));
        cmd1.Parameters["@Name"].Value = this.TextBox1.Text;
        cmd1.Parameters.Add(new SqlParameter("@ProductTypeID", SqlDbType.VarChar, 50));
        cmd1.Parameters["@ProductTypeID"].Value = this.TextBox2.Text;
        cmd1.Parameters.Add(new SqlParameter("@Author", SqlDbType.VarChar, 50));
        cmd1.Parameters["@Author"].Value = this.TextBox4.Text;
        cmd1.Parameters.Add(new SqlParameter("@PublicTime", SqlDbType.DateTime));
        cmd1.Parameters["PublicTime"].Value = System.DateTime.Now;
        cmd1.Parameters.Add(new SqlParameter("@InPrice", SqlDbType.Money, 50));
        cmd1.Parameters["InPrice"].Value = System.Convert.ToDouble(this.TextBox6.Text);
        cmd1.Parameters.Add(new SqlParameter("@OutPrice", SqlDbType.Money, 50));
        cmd1.Parameters["OutPrice"].Value = System.Convert.ToDouble(this.TextBox7.Text);
        cmd1.Parameters.Add(new SqlParameter("@Picture",SqlDbType.VarChar,50));
        cmd1.Parameters["@Picture"].Value=Session["FileNamePic"].ToString();
        cmd1.ExecuteNonQuery();
        conn.Close();
        Page.Controls.Clear();
        Response.Write(TextBox1.Text+"添加成功！");
    }
}

出现如下错误，望大神指正！