Why wont my button stop this thread?

I have an issue with a real time device monitoring threaded app.  I start the thread via btnStart_Click event and it works fine.  When I click on the "Stop button" ( btnStopCalibration_Click ), the screen updates stop, the device continues to monitor and I get an hourglass.  Using debug, I have set breakpoints at all lines within btnStopCalibration_Click and they never hit.  What's going on?  Thank you!




 private void btnStart_Click(object sender, EventArgs e)
        {
            this.EnvironmentalMonitorThread = new Thread(new ThreadStart(this.Start_Environmental_Monitoring));
            this.EnvironmentalMonitorThread.IsBackground = true;
            this.EnvironmentalMonitorThread.Priority = System.Threading.ThreadPriority.Lowest;
            this.EnvironmentalMonitorThread.Name = "Environmental Monitor";
            this.EnvironmentalMonitorThread.Start();
            this.btnStart.Enabled = false;
            this.tcp2701.connect(tcpip);
            if (this.tcp2701.connected)
                this.tcp2701.config();
            if (this.tcp2701.configok)
                this.Start_Environmental_Monitoring();
           
        }



private void Start_Environmental_Monitoring()
        {
            // Initializes equipment and starts the 2701

 
            string name = "Environment";
            int interval = 10;



            object sender = null;
            System.EventArgs e = null;

            long CurTickValue = Environment.TickCount;
            int counter = 0;

            string placeo = "";
            string strStat = string.Empty;

            this.arTimers.Add(new clsTimeCount());
            ((clsTimeCount)arTimers[0]).TargetTime = 10;
            ((clsTimeCount)arTimers[0]).Active = true;
            ((clsTimeCount)arTimers[0]).Starto();


            while (WorkerThreadAlive)
            {

                if (((clsTimeCount)arTimers[0]).Active)
                {
                    Thread.Sleep(100);
                    CurTickValue = Environment.TickCount;

                     if (this.tcp2701.connected)
                    {
                        this.read();
                           
                    }
                   
       
                    ((clsTimeCount)arTimers[0]).StartTime = Environment.TickCount;

               

                }


            }

 private void read()
        {
         Int16 x;
            string[] rawdata;
            double valstring;
           
     
            this.tcp2701.send("Read?");
            this.tcp2701.KI2701Read(ref tcp2701.KIData);
       
            rawdata = this.tcp2701.KIData.Split(new char[] { ',' });
     
                       this.SetAnyText(this.txtip, rawdata[0]);
         
            this.tcp2701.KIInput(ref tcp2701.KIstatus);
            lblinput.Text = tcp2701.KIstatus;
            buffcounter++;
            if (buffcounter >= 20)
            {
                this.SetLabel(this.lblValue, this.txtip.Text, Color.Black, true);
                buffcounter = 0;
            }
            this.Refresh();

           
     
        }

        }


 private void btnStopCalibration_Click(object sender, EventArgs e)
        {
            WorkerThreadAlive = false;
            this.ExposureWorkerThreadAlive = false;
            this.ElapsedTimeWorkerThreadAlive = false;
            try
            {
                this.ElapsedTimeMonitorThread.Suspend();
                this.ExposureMonitorThread.Suspend();
                this.EnvironmentalMonitorThread.Suspend();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
         //  this.StopWorkerThread();
            this.tcp2701.disconnect();



        }