Mine's always been the same. It's always had the non-working Vanilla exe. I feel stupid now! You wouldn't have that security update because support for XP ended last April. THAT'S why it runs on your XP laptop. On your 8.1 machine just look up KB3086255 under "Installed Updates" and if it's there, that would be the reason it doesn't work. All the PTW content has to be there since it's needed for C3C to run, but I've also never had the Civilization3X exe as part of any Gamersgate downloads. I got my PTW No-CD patch from elsewhere. If I had to guess I'd say probably not. I, too, don't care enough to find out since everything is working perfectly now.