I have a Sport Cub S that I had trouble binding with my DX6 a couple times. Once I was too close to the airplane and after I backed up a few more feet it bound ok. Another time I think it was the power up sequence. Rx first then Tx or vice versa. Try these if you haven`t already. You could also try the Radios, Receivers Mfr. Direct Support sub forum near the top here.Hope this helps.