Galois Field conversion issue

Hi every one kindly request your help I am trying to convert the stream r from gf(2^4) to gf(2) in order to use it with the function bchdec e=gf(est_code_pol,1); d=bchdec(e,15,7) it keeps giving me this error

Error using ==> bchdec at 49 Code must be in GF(2).

Error in ==> pgz11 at 156 D=bchdec(e,15,7);

any one can help.

[aya]

And also how can i convert from gf data to binary data