Problem with TThread

Hi, my problem is when I create an instance of TCombinationThread and start the method execute, it do the job but can't access any component of main form... when I try to access, for example, a label or a button, it generate an exception.

the class descending TThread:

type
  TCombinationThread = class(TThread)
  private
    FValue: String;
    FMin, FLevel: Integer;
    FList: TStrings;
    procedure FindCombinations(Value: string; Min, Level: Integer);
  protected
    procedure Execute; override;
  published
    property Value: String read FValue write FValue;
    property Min: Integer read FMin write FMin;
    property Level: Integer read FLevel write FLevel;
    property List: TStrings read FList write FList;
end;

procedure TCombinationThread.FindCombinations(Value: string; Min, Level: Integer);
var
  I: Integer;
begin
  if (Level > 0) then begin
    for I := Min to 25 do
      if frmGerarCombinacao.verifica(I) then
        FindCombinations(Format('%s- %2.2d ', [Value, I]), I + 1, Level - 1);
  end
  else begin
    FList.Add(CuringasText + Copy(Value, 2, Length(Value)));
  end;
end;

procedure TCombinationThread.Execute;
begin
  FindCombinations(FValue, FMin, FLevel);
  Form1.Label1.Caption:='testing'; // for example
  ExitThread(0);
end;

I think that when I try to write or read any component on Main form, it generate the error message.

Please, help me.