Won't recognize that I own packs

I'm a Steam user and almost every other time I open the game it tells me I can't open any of my saves I've been playing in because I don't have the packs required. All of which I have and am sure are installed. It does this even when mods are disabled and it's extremely frustrating because I have to close and reopen the game sometimes several times before it registers the packs I have bought and been using for almost two years.