串口监听程序，总是造成蓝屏重启

我写了一个小程序用于监听串口的数据,第一次点监听,然后暂停,都还正常,但是再点监听的时候就会造成蓝屏死机.我是在虚拟机里面用SerialNull 模拟的串口通信,用别的测试软件通信正常.串口消息是用测试软件发的，监听正常，但是就是在暂停和监听切换的时候会造成蓝屏死机。请大家帮帮忙看看问题在哪里。
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO.Ports;
using System.Threading;


namespace PortTest
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

private SerialPort Sp = new SerialPort();
public delegate void SetTextCallback(string text);
private Thread newThread = null;
string readstr = null;

private void SetText(string text)
{
if (this.textBox_data.InvokeRequired)
{
SetTextCallback d = new SetTextCallback(SetText);
this.Invoke(d, new object[] { text });
}
else
{
this.textBox_data.Text = text;
}

}
private void ThreadProcSafe()
{
this.SetText(readstr);
}
public void Sp_DataReceived(object sender,System.IO.Ports.SerialDataReceivedEventArgs e)
{
byte[] readBuffer = new byte[Sp.ReadBufferSize];
Sp.Read(readBuffer, 0, readBuffer.Length);
readstr =Encoding.UTF8.GetString(readBuffer);


this.newThread = new Thread(new ThreadStart(this.ThreadProcSafe));
this.newThread.Start();
}

private void button1_Click(object sender, EventArgs e)
{
Sp.PortName = "COM4";
Sp.BaudRate = 9600;
Sp.Parity = Parity.None;
Sp.StopBits = StopBits.One;

Sp.DataReceived += new SerialDataReceivedEventHandler(Sp_DataReceived);
Sp.ReceivedBytesThreshold = 1;
try
{
Sp.Open();
button_pause.Enabled = true;
button_listen.Enabled = false;
}
catch
{
MessageBox.Show("端口COM4打开失败！");
}
}
private void button2_Click(object sender, EventArgs e)
{
newThread.Abort();
Sp.Close();
button_listen.Enabled = true;
button_pause.Enabled = false;
}


}
}