Hmm create yoda you have, hmmm?
looks good.
First of all you should use the blur
_smudge tool to get rid off that black and white ridges and maybe fiddle with the contrast value.
I also remembered that the guy from the tutorial converted his image to greyscale, and i got the same errors so i let it stay at 8 bit rgb imageand it worked just fine. you could also adjust the values to -1 and 2 to bring out more maybe that helps other than that i cannot help you, sorry