Starter rope sticking?

I'd been using my mower and stopped the machine to empty the bag. When trying to re-start, the starter rope could not be pulled completely through. With slow , small pulls, the rope eventually released but returned to sticking and the mower did not restart. Has anyone any suggestions on what might be the problem please? The oil is fine and the spark plug new with plenty of petrol in the tank. It is stored in a dry shed usually.