reader callback not working from child form

[jeanvdr]

Hi,
I'm trying to launch a dynamically created demoEid form (from samples) from another form, like this:

procedure TForm1.Button1Click(Sender: TObject);
var
 feid: TForm;
begin
 feid := tfrmMain.Create(self);
 try
  feid.ShowModal;
 finally
  feid.Free;
 end;
end;

Doing so, the reader callback of frmMain is called but not working.

procedure HandleReaderCallBack(var ReaderNumber : DWORD; var EventType : DWORD; UserContext : Pointer); stdcall;
begin
  if Assigned(frmMain) then
    begin
      case EventType of
        1 : begin
              frmMain.Events.Items.Add(DateTimeToStr(Now) + ' card inserted');
              ActivateCardEx(ReaderNumber);
              frmMain.btnReadCard.Enabled := true;
              frmMain.ReadIDCard;
            end;
        2 : begin
              frmMain.Events.Items.Add(DateTimeToStr(Now) + ' card removed');
              DeactivateCardEx(ReaderNumber);
              frmMain.btnReadCard.Enabled := false;
              frmMain.ClearIDData;
            end;
        3:  begin
              frmMain.Events.Items.Add(DateTimeToStr(Now) + ' readers list changed');
              frmMain.btnReadCard.Enabled := false;
              SetCallback(HandleReaderCallBack, nil);
            end;
      end;
    end;
end;

Assigned(frmMain) is false but even if I bypass this test, ActivatedCardEx doesn't work either.
Probably more a Delphi callback problem than a swelio, but can anyone help me on this ?

Thanks