It should be noted that CHU cannot guarantee that you'll be able to get achievements in game. This means that it may be working now, but could be disabled in the future by the developer. We see a developer disabling achievements as much less stressing than them shoving patches to make the trainer not work.
Something has changed on your system within the time frame and most likely has to do with security software or anti-cheat technology by Valve or the game company.
Make sure that you have the trainer whitelisted in your AV and Firewall (alternatively temporarily disable them to make sure this is the cause). Also make sure that anti-cheating technology is disabled (these are usually installed as a Windows Service).