Access violation at address при запуске потоков

procedure TForm3.sButton3Click(Sender: TObject);
var
  i: integer;
begin
 pchecking:=true;
 cproxy:=0;
  for i:=0 to sspinedit1.Value do begin
    SetLength(MyT2, i+1);
    MyT2[i]:=ProxiCheck(True);
    MyT2[i].Priority:=tpLowest;
    MyT2[i].FreeOnTerminate:=True;
    MyT2[i].Resume;
  end;
end;

  private
    MyT2: array of ProxiCheck;

unit Unit4;
 
interface
 
uses
  Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, httpsend, ssl_openssl, blcksock ;
 
type
  ProxiCheck = class(TThread)
  private
    { Private declarations }
  protected
    procedure Execute; override;
    procedure goodproxyfind;
  end;
var
  ipp, pp: String; //ip proxy, port proxy
 
implementation
uses Unit1, Unit3;
 
procedure ProxiCheck.Execute;
var
  httpcheck: THTTPSend;
  b1,b2: integer;
  str, site: string;
  x: Integer;
  a1: string;
begin
  while form3.pchecking do begin
    httpcheck:=THTTpSend.Create;
    PCS.Enter;
    Str := form3.sMemo1.Lines[form3.cproxy];
    x := Pos(':', Str);
    ipp := Copy(Str, 1, x - 1);
    pp := Copy(Str, x + 1, Length(Str));
    form3.cproxy:=form3.cproxy+1;
    Pcs.Leave;
 
    httpcheck.HTTPMethod('get', 'http://www.myip.ru/');
    site:=httpcheck.Document.ToString;
    b1:=Pos('Ваш IP-адрес</B></TD></TR><TR><TD bgcolor=white align=center valign=middle>',site)+75;
    Delete(site,1,b1-1);
    b2:=Pos('</TD></TR>',site)-1;
    a1:=Copy(site,1,b2);
 
    if a1=ipp then Synchronize(goodproxyfind);
 
  end;
end;
 
procedure ProxiCheck.goodproxyfind;
begin
   form3.sMemo2.Lines.Add(ipp+':'+pp)
end;
 
end.

SetLength(MyT2, i+1);
    MyT2[i]:=ProxiCheck(True);
    MyT2[i].Priority:=tpLowest;
    MyT2[i].FreeOnTerminate:=True;
    MyT2[i].Resume;