Kill fox-Toolkit while initialize

Hello,
currently I run against a problem with Fox-Toolkit.
I try to end a dialog while it is intialized.

Code:
KDataFOXLibDlg::KDataFOXLibDlg(FXApp *app, const FXString &title)
: FXDialogBox(app, title, DECOR_ALL, 0, 0, 600, 500, 0, 0, 0, 0, 0, 0)
{

int res = 0;
if(res == 0){
FXMessageBox::error(app, MBOX_OK, "Messagebox", "Error");
::exit(0); //::exit(1);
}

// Set global fxapp to SDK
res = ::SetFXApp(app);
// Cut heret to keep clean
}

I will always get an error that I try to create a Window before parent
window was created.
I do not understand this behavior because it is always possible to
create a MessageBox on the Desktop handle. Iam not happy with the fact
that I cannot stop the app without tell the user why the app cannot
start.
Is there a workaround?