THQ has asked Metro 2033 fans to be patient while it works out what caused a bug that stops Achievements unlocking properly.
Earlier this month THQ released the Ranger Pack on Xbox 360 adding a new harder game mode. Unfortunately though it also made it impossible to redeem Achievements to do with the DLC or the whole game, depending on which forum you believe.
"We understand some people are still experiencing issues with achievements unlocking in the Metro 2033 Ranger Pack DLC," the publisher said in a statement carried by Joystiq.
"We are currently working with Microsoft to ascertain whether this is due to a code related issue with the DLC itself, or an error in the Marketplace process whereby the DLC was added to Xbox Live Marketplace before the new achievement data was added - this exact issue has happened to other games in the past, but we need to be sure that this is what's happening here.
"We realise this is frustrating for those of you who have been waiting to enjoy the Ranger Pack DLC, and we ask for your patience as we try to pinpoint the exact issue and solution."
In the meantime you could always play Metro 2033 again. We rather liked it - it's a gritty, atmospheric shooter set in a post-apocalyptic Moscow subway system.