Earlier, I used to run Windows 7 ultimate 32 bit on my pc. I purchased the Vanilla version of Civ 5 at that time (Expansion was not out yet). Later I had to upgrade to 64 bit Win 7. Civ 5 stopped working and a message was displayed that it is not compatible with a 64 bit OS. Is the same true for its expansion pack. Can I run Civ 5 Brave New World on Win 7 64 bit?
Civilization 5 is a 32 bit game that runs on 32 bit and 64 bit systems.
I have installed and run Civ 5 on 64 bit Windows 7, Windows 8 and Windows 10 with no problems - there were no separate installers required for 64 bit system.
I strongly suggest to back up your saved games, uninstall the game and reinstall.
If that fails please can you post the exact wording or preferably a link to a screenshot of the error message?
I've run Civilization V - Brave New World on a 64 bit Windows 7 machine without any issues, so yes, it is 64 bit compatible.