//In my main form I have this

  DBManager : TDBManager;

procedure TFrmMain.FormCreate(Sender: TObject);
begin
  DBManager.Create(IBDB, IBTrans);
  DBManager.Open;
end;


//And in my other unit file, I have this :

  type PIBDatabase = ^TIBDatabase;
  type PIBTransaction = ^TIBTransaction;

  type TDBManager = class
    private
      IBDB : TIBDatabase;
      IBTrans : TIBTransaction;

    public
      constructor Create(_IBDB : TIBDatabase; _IBTrans : TIBTransaction);
      procedure Open();
  end;

constructor TDBManager.Create(_IBDB : TIBDatabase; _IBTrans : TIBTransaction);
begin
  IBDB := _IBDB;    // Here is the error
  IBTrans := _IBTrans;
end;