As soon as the eagerly-awaited patch 1.5 was installed, fans started reporting a game-killing bug: earlier savegames were rendered useless and could not be played. Irina Kassina summed up the situation like this.

Limbic said they had not encountered this bug during their testing, called their guys in and worked through the night to fix it. Running the updater at this point will get you to the "hotfix" version 1.5.1, which is reported to work fine. Old saves from 1.4 will now work, though new saves from the 1.5 version will not. Those are only one day old, though. Kudos to Limbic for the quick fix. I know some developers who would not be so quick...