If you've set VoiceAttack up to run as an admin through Windows' properties, that will not work as Windows will not allow apps to launch at startup as an administrator in that way (without creating scripts or scheduled tasks).
You will want to go into VA's Options, over to the System/Advanced tab and select 'Run VoiceAttack as an Administrator'. Make sure to undo your settings through Windows' properties as well.
Hope that helps!