Unity 3D调用System.Windows.Forms.dll 提示 could not register the window class ,win32 error 0

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System.IO; 
using UnityEngine.UI;
using System;
using System.Threading;
using System.Linq;

public class WindowFormsShowModelPath : MonoBehaviour
{ 
    string str_path = "";
    string modelname = "";

    private void Start()
    { 
        OopsWindowsThreadStart(); 

        System.Windows.Forms.MessageBox.Show("start..."); 

        ThreadRunning = false;
    }
    private void Update()
    {
        if (Input.GetKeyDown(KeyCode.P))
        {
            OopsWindowsThreadStart();

            System.Windows.Forms.OpenFileDialog Dialog = new System.Windows.Forms.OpenFileDialog();
            Dialog.Filter = "文件(*.FBX)|*.FBX";

            if (Dialog.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                str_path = Path.GetDirectoryName(Dialog.FileName); 

                modelname = Path.GetFileNameWithoutExtension(Dialog.FileName); 

                System.Windows.Forms.MessageBox.Show(str_path + "\\" + modelname); 
            }
            else
            {   
                str_path = "";
                modelname = "";
                System.Windows.Forms.MessageBox.Show(null...); 
            }
            ThreadRunning = false;
        }
    }


    #region Close Window Oops

    private System.Threading.Thread CloseOops;
    private bool ThreadRunning = true;
    private void OopsWindowsThreadStart()
    {
        CloseOops = new System.Threading.Thread(ClearOopsWindows) { IsBackground = true };
        ThreadRunning = true;
        CloseOops.Start();
    }
    private void ClearOopsWindows()
    {
        while (ThreadRunning)
        {
            FindAndCloseWindow();
        }
    }

    [System.Runtime.InteropServices.DllImport("user32.dll")]
    public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
    [System.Runtime.InteropServices.DllImport("user32.dll")]
    public static extern int SendMessage(IntPtr hWnd, uint Msg, int wParam, int lParam);

    public const int WM_SYSCOMMAND = 0x0112;
    public const int SC_CLOSE = 0xF060;

    public static void FindAndCloseWindow()
    {
        IntPtr lHwnd = FindWindow(null, "Oops");
        if (lHwnd != IntPtr.Zero)
        {
            SendMessage(lHwnd, WM_SYSCOMMAND, SC_CLOSE, 0);
        }
    }
    #endregion
}