C#控件大小随窗体变化而变化，利用网上这段代码写了一个界面，之前电脑运行正常。目前Debug运行也没有问题，可是现在VS只要运行程序里面一个Form就会报错NULL，莫名其妙不知怎么回事？

①这是我之前用VS2015编译好的程序，直接运行没有问题
②这是里面Form的代码（控件大小随窗体变化而变化）

    private float X;
    private float Y;
    private void setTag(Control cons)
    {
        foreach (Control con in cons.Controls)
        {
            con.Tag = con.Width + ":" + con.Height + ":" + con.Left + ":" + con.Top + ":" + con.Font.Size;
            if (con.Controls.Count > 0)
                setTag(con);
        }
    }
    private void setControls(float newx, float newy, Control cons)
    {
        foreach (Control con in cons.Controls)
        {
            string[] mytag = con.Tag.ToString().Split(new char[] { ':' });
            float a = Convert.ToSingle(mytag[0]) * newx;
            con.Width = (int)a;
            a = Convert.ToSingle(mytag[1]) * newy;
            con.Height = (int)a;
            a = Convert.ToSingle(mytag[2]) * newx;
            con.Left = (int)a;
            a = Convert.ToSingle(mytag[3]) * newy;
            con.Top = (int)a;
            Single currentSize = Convert.ToSingle(mytag[4]) * Math.Min(newx, newy);
            con.Font = new Font(con.Font.Name, currentSize, con.Font.Style, con.Font.Unit);
            if (con.Controls.Count > 0)
            {
                setControls(newx, newy, con);
            }
        }
    }
    private void Form15_Resize(object sender, EventArgs e)
    {
        float newx = (this.Width) / X;
        float newy = (this.Height) / Y;
        setControls(newx, newy, this);
        this.Text = this.Width.ToString() + "" + this.Height.ToString();
    }
    private void Form15_Load(object sender, EventArgs e)
    {
        this.Resize += new EventHandler(Form15_Resize);
        X = this.Width;
        Y = this.Height;
        setTag(this);

        this.textBox1.Text = "0°0′0.000″";
        this.textBox2.Text = "0°0′0.000″";
        this.textBox3.Text = "0.00";
        this.textBox4.Text = "0.00";
        this.textBox5.Text = "0-00-00 00:00:00";

        timer3.Enabled = true;
        timer3.Start();
        timer4.Enabled = true;
        timer4.Start();
        timer5.Enabled = true;
        timer5.Start();
    }

③现在只要单独运行这个Form15就报错
namespace BDEH
{
static class Program
{
///
/// 应用程序的主入口点。
///
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form15());
}
}
}
④这是报错的界面

之前以为是换电脑重装VS的原因，可是后来排查了几天，换了电脑系统也是一一样，真是奇怪了。而且我专门又建了一个项目，只运行这段代码，也是不行。求高手解答

图上不是有吗，con.Tag null