Sysprep is only allowed to be ran a total of 2-3 times (memory is failing me as it is late). Read up on it's limitations, when I was using WDS to distribute server images I always kept a copy of the image with all installed applications etc, but BEFORE I ran sysprep to avoid issues. That way I could just make changes to it when needed, copy it to a new image file and then run sysprep before deploying the image.