Solved it by playing another game - telling it to force quite the active game - which bugged out - but eventually let me do stuff without the error message. I think it had to do with running 'FlyInside P3d' for running flight sims inside Oculus. Untested territory - but pretty cool!
This just happened to me too. Nothing was running. Launching another game (which Oculus did grudgingly as it told me I had another app running) then closing it solved it. I hadn't even played an Oculus game for at least 14 hours. Definitely very buggy.