Access violation at

procedure TForm4.FormCreate(Sender: TObject);
var
  i,j:integer;
begin
  for i:=1 to 20 do
  for j:=1 to 20 do
  begin
  Field[i,j]:=TImage.Create(form4);
  field[i,j].Parent:=Form4.Panel2;
  field[i,j].Canvas.Brush.Color:=clRed;
  field[i,j].Canvas.Pen.Color:=clRed;
  Field[i,j].Top :=-25+25*i;
  Field[i,j].Left :=-25+25*j;
  end;
 
  for i:=1 to 100 do
  for j:=1 to 100 do
  begin
  basement[i,j]:=Char(random(9));
  changefield(i,j,basement[i,j]);
  end;
end;
 
procedure changefield(j,k:integer;letter:char); 
begin
Form4.field[j,k].Canvas.Refresh; //Вот отсюда идут ошибки, пока не удалю код до...
Form4.field[j,k].Canvas.Brush.color:=clWhite;
Form4.field[j,k].Canvas.Font.Size:=15;
Form4.field[j,k].Canvas.TextOut(7,1,letter); //..сюда
drawframe(j,k);
end;
 
procedure drawframe(a,b:integer);
BEGIN
Form4.field[a,b].Canvas.Pen.Color:=clBlack;
Form4.Field[a,b].Canvas.Pen.Width:=3;
Form4.Field[a,b].Canvas.MoveTo(0,0);
Form4.Field[a,b].Canvas.LineTo(25,0);
Form4.Field[a,b].Canvas.LineTo(25,25);
Form4.Field[a,b].Canvas.LineTo(0,25);
Form4.Field[a,b].Canvas.LineTo(0,0);
end;