Ошибка в игре 15-ки

var
  Form1: TForm1;
i,j:integer;
n:integer;
implementation
 
{$R *.dfm}
 
procedure TForm1.Pole;
begin
n:=1;
for i:=0 to 3 do
for j:=0 to 3 do
begin
StringGrid1.Cells[i,j]:=IntToStr(n);
 
if n=16 then
StringGrid1.Cells[i,j]:='';
 
if n<=15 then
inc(n);
end;
end;
 
procedure TForm1.StringGrid1SelectCell(Sender: TObject; ACol,
  ARow: Integer; var CanSelect: Boolean);
begin
if StringGrid1.Cells[ACol,ARow]<>'' then
if (StringGrid1.Cells[ACol+1,ARow]='') or (StringGrid1.Cells[ACol,ARow+1]='') or (StringGrid1.Cells[ACol-1,ARow]='') or (StringGrid1.Cells[ACol,ARow-1]='') then // [COLOR="Red"]Вот здесь иногда выдает ошибку[/COLOR]
if (ACol<=3) and (ARow<=3) then
for i:=0 to 3 do
for j:=0 to 3 do
begin
if StringGrid1.Cells[i,j]='' then
begin
StringGrid1.Cells[i,j]:=StringGrid1.Cells[ACol,ARow];
StringGrid1.Cells[ACol,ARow]:='';
end;
end;
end;
 
procedure TForm1.FormPaint(Sender: TObject);
begin
Pole();
end;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
i:=4;
for j:=0 to 3 do
StringGrid1.Cells[i,j]:=IntToStr(random(255));
j:=4;
for i:=0 to 3 do
StringGrid1.Cells[i,j]:=IntToStr(random(255));
end;
 
end.

procedure TForm1.StringGrid1SelectCell(Sender: TObject; ACol,
  ARow: Integer; var CanSelect: Boolean);
begin
StringGrid1.Cells[ACol+5,ARow+5]:='45456';
end;