The only other thing that I can think of that might cause this, is that you need to upgrade your Sound Blaster 128 cards drivers. Make sure that they are the current version, or that they at least support DirectX 7.0a. The easiest would be to go to
www.creative.com and just update to there latest drivers for that card.
If this doesn't work, you might want to try uninstalling your Sound Card and then reinstalling it, to see if maybe something is not installed correctly.