Fabio,
You should not be trying to use a global OKL handler for this task, use the form.KeyPress() method with form.KeyPreview set to .t. instead.
You always have to write code to verify that _screen.ActiveForm actually refers to a form at the instant you are trying to use it.
>release a form with OOP need to call form.release method.
>
> PROCEDURE Activate
> ON KEY LABEL CTRL+F11 _SCREEN.ActiveForm.Release
> ON KEY LABEL CTRL+F12 RELEASE WINDOWS _SCREEN.ActiveForm.Name
> ENDPROC