Pure virtual function error?

[Nayomiboo]

Pure virtual function being called while application was running (GIsRunning == 1).

That's what I keep getting before it crashes and I have no idea what it means. I'm not running anything else while playing this either, it's just Exp 33. Before I could get about an hour of playtime in before it did that. This time I barely got five minutes in. I'd really like to keep this game rather than getting a refund and I'm close to the two hour mark that would stop Steam from refunding it anyways. Does anyone know a way to fix this?