Windows 7 - The Witcher and BioShock issues

Hi,

I freshly installed Seven RC1 7100 x64 on my computer, because I've got tired of XP x86.

I tried to setup The Witcher, but each time I try and whatever compatibility mode I use, I get the same failure message (something about "checking if the game is a 32bit or 64bit").

About BioShock, I managed to install it with not much difficulty, but then, when trying to launch it, I get the same message.

Yet, it seems that both games are running just fine with some other people so I was wondering if I was missing something, or if I'm just experiencing bad luck.

Thank you in advance for your help !