This is really weird. Let's go through the basics: What type of Civ4 installation do you have? Is it the normal game with BTS as a separate expansion? Or are you using CivComplete/Gold? Did you get it from Direct2Drive or Steam or some "other" source (I don't care or need to know where, just want to know what might be different)? Have you patched BTS to at least 3.13? From the main menu, can you click ADVANCED and then ABOUT THIS BUILD and take a screenshot? Did you install BUG as a mod this second time around? And the game works without BUG, right? Are you running Vista or XP? Are you using a foreign language O/S installation? Is there anything non-standard about your system or setup?