AvatarWA

I had the same problem. When I reinstalled Windows 7 on my computer, I installed Java version 8 (the latest) which is fine for Minecraft 1.8 Voltz, however uses Minecraft 1.6.4 which needs Java version 7. Installing Java 7 alongside Java 8 fixed the problem and I am now able to play Voltz again :-) Good Luck.