Portal 2 (Linux)
I had this problem on 64 bit Ubuntu 14.04 and fixed it by doing the following
Delete SteamApps/common/Portal 2/bin/libstdc++.so.6 Run the Steam client cd "SteamApps/common/Portal 2" LD_LIBRARY_PATH=bin ./portal2_linux -game portal2 -windowed
After running it once this way I could start it from the normal library window
I am sorry that I do not remember the attribution of this answer, but you may be able to google it up if you wish.