Invalid class typecast

type
  TSegment = class(TObject)
  private
    FId: Integer;
    FNazwa: String;
    FTyp: Integer;
  public
    constructor Create(Aid: Integer; Anazwa: String; Atyp: Integer);
    destructor Destroy;
    property id: Integer read FId write FId;
    property Nazwa: String read FNazwa write FNazwa;
    property typ: Integer read FTyp write FTyp;
  end;

  TSegmentList = class(TObjectList)
  private
    function GetItem(aindex: Integer): TSegment;
    procedure SetItem(aindex: Integer; const Value: TSegment);
  public
    constructor Create(AOwner: bool);
    destructor Destroy;
    procedure pobierzSegmenty(Query: TZQuery);
    property Items[aindex: Integer]: TSegment read GetItem
      write SetItem; default;
    function Add(ASegment: TSegment): Integer;
    function FindItem(Anazwa: String): TSegment;
  end;

function TSegmentList.FindItem(Anazwa: String): TSegment;
var
  tempSegment: TSegment;
  I: Integer;
begin
  try
  tempSegment := TSegment.Create(-1,'',-1);
  result := tempSegment;
  for I := 0 to self.Count -1 do
    if self.Items[I].Nazwa = Anazwa then
    begin
      FreeAndNil(tempSegment);
      tempSegment := TSegment.Create(self.Items[I].id, self.Items[I].Nazwa,
        self.Items[I].typ);
      //tempSegment := self.Items[i] as TSegment;
      Result := tempSegment;
      break;
    end;
  except
    on e:exception do fmMain.ObsluzBlad(e,'TSegmentList.FindItem','');
  end;
end;

{dodano 08/09/2011}

function TSegmentList.Add(ASegment: TSegment): Integer;
begin
  Result := inherited Add(ASegment);
end;

destructor TSegmentList.Destroy;
begin
  inherited Destroy();
end;