Рисование рандомных линий: ошибка в коде

void PaintEllipse()
{
while(!fTerminate)
{
int iRed=rand.Next(255);
int iGreen=rand.Next(255);
int iBlue=rand.Next(255);
Pen myPen = new Pen(Color.FromArgb(iRed,iGreen,iBlue),3);
int iX=rand.Next()%this.Size.Height;
int iY=rand.Next()%this.Size.Width ;
int iWidth=rand.Next(500);
int iHeight=rand.Next(500);
g.DrawEllipse(myPen,iX, iY,iWidth, iHeight);
Thread.Sleep(500);
}
}
void PaintRect()
{
while(!fTerminate)
{
int iRed=rand.Next(255);
int iGreen=rand.Next(255);
int iBlue=rand.Next(255);
Pen myPen = new Pen(Color.FromArgb(iRed,iGreen,iBlue),3);
int iX=rand.Next()%this.Size.Height;
int iY=rand.Next()%this.Size.Width ;
int iWidth=rand.Next(500);
int iHeight=rand.Next(500);
g.DrawRectangle(myPen,iX, iY,iWidth, iHeight);
Thread.Sleep(500);
}
}
void PaintLine()
{
while(!fTerminate)
{
int iRed=rand.Next(255);
int iGreen=rand.Next(255);
int iBlue=rand.Next(255);
Pen myPen = new Pen(Color.FromArgb(iRed,iGreen,iBlue),3);
int iX1=rand.Next()%this.Size.Height;
int iY1=rand.Next()%this.Size.Width ;
int iX2=rand.Next()%this.Size.Height;
int iY2=rand.Next()%this.Size.Width ;
g.DrawLine(myPen,new System .Drawing
.Point(iX1,iY1),new System .Drawing .Point(iX2,iY2));
Thread.Sleep(500);
}
}
Graphics g;
Random rand;
int i=0;
bool fTerminate;
Thread[] T;
using System.Threading;
private void Form1_Load(object sender, System.EventArgs e)
{
g = this.CreateGraphics();
rand=new Random ();
fTerminate=false;
T = new Thread[ 3 ];
}
private void Form1_Paint(object sender , System. Windows. Forms.
PaintEventArgs e)
{
fTerminate=false;
T[0] = new Thread(new ThreadStart(PaintEllipse));
T[0].Start();
T[1] = new Thread(new ThreadStart(PaintRect));
T[1].Start();
T[2] = new Thread(new ThreadStart(PaintLine));
T[2].Start();
}
private void Form1_Closing(object sender, System. ComponentModel.
CancelEventArgs e)
{
fTerminate=true;
for(int j=0;j<3;j++)
T[j].Abort ();
}
protected override void Dispose( bool disposing )
{
fTerminate=true;
for(int j=0;j<3;j++)
T[j].Join();
if( disposing )
{
if (components != null)
{
components.Dispose();
}
}
base.Dispose( disposing );
}
Monitor.Enter( g);
try
{