This error shows up as "SteamError_UnableToRefreshSession" in game. Normally this is an issue with Steam Authorization being temporarily unavailable.
Solution: Restart your Steam client.
If this continues to provide trouble, the following steps below might be necessary:
1. Restart you computer.
2. You can find instructions to repair your install here.
3. If that doesn't fix it, please contact our team with your log files. Instructions for that are here.