So after several hours of being completely unable to get the chain to stay in any gear on a 12-27 cassette I called Bike Sports, then I counted what was taken off the bike on an old cassette and what was put on, 8 came off and 9 were put on, an 8 speed chain is wider than a 9 speed??? thereby accounting for the inability to change gear???
Now you should replace an 8 speed with an 8 speed right?