If commands are recognized, and the command target is set correctly (I.E. you're using "Active Window" and the application already has focus, or you're targeting the window explicitly), keypresses are being sent to the target application. Whether that application handles those keypresses correctly is not up to VoiceAttack itself.
Especially at lower or inconsistent framerates, games may have trouble registering keypresses reliably. Try increasing the press time further.
Also note that the pause between keypresses is important; If you're sending multiple presses in rapid succession (especially without an explicit pause in-between), they may be ignored by the target application.