errors using cdf function

This error occurs when you include a file twice!

I assume you're using the Normal CDF function. What does your main.cpp file look like. Make sure you don't include poly_eval.h and errorfn.h explicitly. You should only have:

#include <codecogs/stats/dists/continuous/normal/cdf.h>

Can you post your code here (or perhaps a cut down version that still exhibits this error)