The original charmm force field was downloaded from MacKerell Lab. Please download the force field release from there, and replace the following files
aminoacids.rtp
forcefield.itp
ions_at_type.itp
ions.itp
In aminoacids.rtp, the listed amino acids have been scaled.
ASP
LYS
GLU
ARG
K+, Na+, Cl- with radius corrected sigma were added to ions_at_type.itp, and included in forcefield.itp. New moleculetype for ions were added to ions.itp.