In an attempt to crack down on international game trading, Valve "Region Locked" several games, some retroactively, rendering them unusable if you've traded them with a person from a different region. This move was made in response to the common practice of trading games with users from regions where they are available for considerably less.
The list of games confirmed to be locked in the store is as follows:
The list of games confirmed to be locked retroactively is as follows:
RustBanished7 Days to DieThe Banner Saga- Thief
- South Park
- Hawken
Hegemony Rome: The Rise of CaesarDivinity: Original SinKerbal Space ProgramAssetto CorsaDeadfall Adventures- Men of War Assault Squad 2
Payday 2Injustice: Gods among Us
If you've traded any of those games, it is advised that you check whether they are functional and can be activated if received as a gift. It's also recommended that you hold off from trading any of those titles before the matter is clarified by Valve.
BanishedRust- South Park
- Thief
Kerbal Space Program- Hawken
What can I say? That's naughty, that's very naughty, Valve. Region locking content? Digital content? In the 21st century? Really? Especially retroactively - I can understand locking games in the store, fair play, but after they were traded, so that the gift can't be activated? That's bogus.
Update: Several games from the list have now been unlocked - it's possible that the Steambot responsible for Region Locking simply went nuts for a while and the situation was amended later. Yay! Well... partially - some games remain locked.
Source #1, Source #2, Source #3 (Update)