DLL i MDIChild - problem

library mag;


uses
  SysUtils,
  Windows,
  Forms,
  Classes,
  Sharemem,
  mag_frm in 'mag_frm.pas' {mag_f};

var
dllapp : TApplication;

{$R *.res}

procedure show_mag(MainApp : Tapplication); 
var
magf     : Tmag_f;
begin
if not Assigned(DllApp) then begin
DllApp := Application;
Application := MainApp;
end;
magf := Tmag_f.Create(MAinapp);
magf.Show;

end;

procedure MyDLLProc(Reason: Integer);
begin
if Reason = DLL_PROCESS_DETACH then
if Assigned(DllApp) then
Application := DllApp;
end;

exports

show_mag name 'show_mag';

begin
DLLProc := @MyDLLProc;
end.

var
  MainForm: TMainForm;
 procedure show_mag (MainApp : TApplication);external '..\DLL\mag.dll';

procedure TMainForm.ToolButton2Click(Sender: TObject);

begin
show_mag (application);

end;