Just download the Oculus setup exe and choose Repair. Should solve your problem.
I've had the same Runtime Service error off and on for a few months now. I came across a blog post the other day recommending to select the 'repair' option from the Oculus installer, but that didn't actually fix anything. I'm still getting the error here and there. I can literally open Oulus, play a game, then close it to grab lunch. After lunch, I'll try to re-open Oculus...it gives the error, even though the pc hasn't even rebooted from the last time I used the Rift. I can fix it by going into 'services', then right-clicking OVRService, and selecting 'start'. But the error will still randomly show up again a few sessions down the road. I'm starting to think it's a Windows issue.