I dremelled the square corners off of the teeth to allow the chain to roll off of the sprocket smoother. Just break the edge a little and you can file it if you don't have a dremel.
Yeah, check the chain alignment (front and rear sprockets must be in line and on the same plane so there is no torsion on the chain), and check chain tension. I had the same problem recently and it was chain alignment. I am using 415 chain, which came stock from the undisclosed location of the Chinese bike chain factory.