When I exit rF2, Steam says it is still open. I have to manually quit it from the steam app and clicking on the proper button I receive this message
well then, honestly i've never seen that error and have no idea, try a integrity check through steam.
before you go and uninstall the entire game, try just renaming the player.json file. Let rF2 rebuild the file on your next start up and MAYBE that will help.(just a shot in the dark)