Check the signature of the createFit function. Does it actually return something? i.e. if the signature is just:
function createFit(x,y)
then you will get the too many output arguments error since the above code is
n=createFit(x,meanValue);
i.e. the code is trying to get the return value of a function that does not return anything. There seems to be different versions of createFit on the MATLAB FileExchange and elsewhere too, so please verify that you are using the expected/correct version. I was able to reproduce your error using the code found at http://code.google.com/p/prosilica/source/browse/trunk/MATLAB/createFit.m?r=36
