This explanation is for version 0.2.1(upcoming update)

After version 0.2.1, you can no longer transfer save files from versions older than 0.1.9 to this game version. If you want to use older save files (from version 0.1.8 and below), you need to play on version 0.1.9 or 0.2.0. Alternatively, you can simply start a new game with this version.Note: To clarify, save files from versions 0.1.9 and 0.2.0 will remain compatible with future updates.This restriction only applies to save files from version 0.1.8 and earlier. I dont think anyone will use a save 2 versions older but still its a important note if you decide to use.