Hello,
Same problem, error 55 when launching the game.
I have several times reinstall steam and Civilization 5, but i still the same problem.
1) When downloading the game or launch, steam is extremely slow and there are important lag on my pc.
2) the download announced just over 5 GB, but when I get to access the download, there adverts only 4.7 GB.
The problems started at the last update, I've never had any problem to run civilization 5 before.
I have no problems with to another steam game (Team Fortress 2, earth 2160, Red Orchestra and empire total war).
Pleaze help.
I've noticed that my issue is with avast!, once i completely turned off avast! I managed to "complete" the insallation, however, while not able to play the game, i'm now experiencing severe lags, however, a friend pointed that it could be due to playing with 12 civs, 24 states on a huge earth map, which is understable, but it got the point that it just lag too much for me.
Gonna have to find another way to get the achieveemnt!