I download this game yesterday and found that it just wouldn't play. Allowed me to activate the product, but when I clicked play, it would say preparing to launch and then ... nothing. Eventvwr showed an 0x000005 error. Cleared out the cache files and downloaded again; same thing.
I then did the usual google search and tried suggested fixes including, reinstall directx 9 and visual C++ 2005 as well as setting the EXE to run as administrator; still nothing.
Then I noticed that many other people with the problem all had Windows 7. So I set the Cities_XL executable to compatibility mode Windows Vista SP2 and now it works perfectly.
As I say, not a perfect fix, but if anyone else is pulling their hair out .......