Работа с MDIChild в Delphi 7

procedure TForm1.Button2Click(Sender: TObject);
begin
form2.show;
end;

procedure TMain.ToolButton21Click(Sender: TObject);
begin
Pokupately.Show;
end;

procedure TMain.ToolButton21Click(Sender: TObject);
begin
MDIChildren[1].Show;
end;

Pokupately.Show

Показать форму Pokupately

Project Pokupatel.exe raised exception class EAccessViolation with message 'Access violation at address 0047A0E6 in module 'Pokupatel.exe'. Read of address 000002F4'. Process stopped. Use Step or Run to continue.

TPokupately.Create(Owner);

procedure TMain.N8Click(Sender: TObject);
begin
If n7.Tag = 0 then
begin
TPokupately.Create(Owner);
N7.Tag:=1;
IF Prava_d.Pr=true then
begin
N14.Enabled :=true;
N15.Enabled :=true;
N16.Enabled :=true;
ToolButton1.Enabled :=true;
ToolButton3.Enabled :=true;
ToolButton4.Enabled :=true;
end;
end
Else MessageBox(Handle,'Форма уже открыта','Внимание',Mb_OK+MB_ICONINFORMATION);
end;

procedure TMain.ToolButton22Click(Sender: TObject);
begin
Pokupately.Show;
end;

if Pokupately <> nil then Pokupately.Show;