I received an answer from the tech already, only after about 4 hours. Although it was in french, it DID give me a new password to try, which now works fine. So, my problems are solved, game is working, and rather a quick repsonse.
I have done exactly the same thing, caps in username and now can't play the game - I just got it today. I have tried no caps in log in screen, to no avail. I also tried allowing specifically the CitielXL.exe and CitiesXL_game.exe files through my firewall (windows 7 64), and running as admin. I did send a message to tech support, but by the sounds of things I won't be playing this game anytime soon. Unable to create a new username as the product key is now registered to my first (apparently broken) account. Looks like some exspensive landfill, even though I got it on sale.