[delphi.com.ar]

Si la unit1 utiliza cosas de la unit2 solo en la implementation, no utilices la unit2 en la interface sino en la implementation

unit Unit1;

interface

Uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms;

...

implementation

uses
  Unit2;


procedure Tgb_fmSerieTX.cmdSalirClick(Sender: TObject);
begin
  form2.show
end;

end.

Saludos!