The CHARMM force field release never contained a file named "toppar_all27_prot_na.toppar". Also, I believe CHARMM-GUI already transitioned to the CHARMM36 version of the force field. That version is modular, meaning you can read in any combination of parts of the force field (protein, carbohydrate,...)
Generally spoken, it is advisable to read the the "sticky topics" of a forum (marked by this icon:
) before posting on that forum, as stipulated by the Parameter Set Discussion guidelines
and the general guidelines for the CHARMM forums
. For example, there is a sticky topic on how to download the CHARMM36 force field
CHARMM force field: accept no substitutes!