Despite being highly playable, RimWorld is only in alpha. A major update was released, and this means old save files will crash and burn.
I do have the option install the previous version, but I'm not sure it will be worth the effort. RimWorld is meant to be played in short bursts with a "see-how-long-I-can-last" mentality.
I've learned a lot from my first colony, and I look forward to the next.