The random uninstall is apparently a Steam issue. Steam's support page has an article about it (
https://support.steampowered.com/kb_...8379-RYIP-2998), but it's not particularly helpful - it just tells you to reinstall and blames external hard drives, which may account for some of the problems - but I know from personal experience that using external HD's can't be the only cause, because I've had the problem with games on my regular drive.
The Invalid Database Version message usually means you're trying to use a save created with a newer version than the one you're using (not possible if you just reinstalled) or there's corruption in one or more save files. If you can upload it (
instructions here), I'll have a look and see if it's fixable.