Huh, that's a weird crash. No idea what caused it, but it's basically saying your world doesn't have an overworld, or, at least, that it can't load it. Was there any dimension scurvying you did last time you played that world? Which modpack is this?
the first time i loaded the world after updating the ftb launcher my world crashe when i load my save. it says building terrain for about five mins then crashes.
If you have Optifine installed remove it and see if it loads then. If you want Optifine in the future you need to use the preview version and get a matching Forge from Forge's downloads yourself.
