can't read "NS": no such variable while executing in GIT-GUI

This issue arise due to incompatible text conversion soft like -- for not founding the libidn , zlib,
curl. And this issue is available on every other version of git that are lower from 1.7.5.
So manually build and install the git-1.7.5 and fix your problem.
yum install gettext-devel expat-devel curl-devel zlib-devel openssl-devel
cd /usr/local/src
tar xzvf git-1.7.5.tar.gz
cd git-1.7.5
make prefix=/usr/local all
make prefix=/usr/local install
After that you need to install git-gui by --
yum install git-gui
So now you can use real git in git-gui.