Windows.Form not fire keyDown event

private void screensaverWindow_Load(object sender, System.EventArgs e)
{            
    this.BringToFront();            
    this.Focus();
    this.KeyPreview = true;
    this.KeyDown += new KeyEventHandler(onkeyDown);            
}        

onKeyDown() is never called. Any idea why?

EDIT: This works in release mode!? I guess it must be visual studio debugger interfering somewhere