Thanks for the response Aarik,
I checked the build number. it seems to be the newest avaiable - 1.0.6.0617. I even ran the "verify integrity of game cache" in Steam. I got the message there is 1 file that will be reaquired. Unfortunately, the problem still occurs. I even tried to remove all the saves and put the old ones from 1.0.5 to let the game convert saves again. The Wall of Flame still does no damage.