Ahhh poly to subd error an oldie but a goodie. I havent used subds for years since smooth poly became the norm

Usually this error can stem for a few things. Could be due to extra polys or verts accidently misplaced here and there, it can also be a build up of blind data on the subd itself. This can be found by opening up the hypergraph and selecting the object and graphing it. You'll either have subd blind data nodes or you wont. If you do have them select them and delete them its that easy. But beware as the mesh may disappear so you'll have to select it and reassign a shader.

cheers
Jay