There was a very small group of "conspiracy" types who thought Paul had died back in the 60's and replaced by a look-alike. I remember one of the "tell-tale" signs was that on the Abbey Road Album cover, he's shown walking barefoot, which I guess is some sort of symbol in England for being dead.
But the whole thing started up again within the last year when some British publication, similar to the Onion, concocted a fake interview with Ringo Starr who supposedly "fessed up" and finally admitted that McCartney was dead and that they had recruited another person to play the part of McCartney. It was all tongue-in-cheek, but like so many Onion stories, people read it and believed it and the 50 yr old conspiracy theory blew up again.