please post the content of your files /etc/yum.repos.d/rpmforge.repo and /etc/yum.repos.d/mirrors-rpmforge
have you followed a guide to install the rpmforge repos? Maybe someting like
How are your DNS settings?
try the folowing commands and post the output:
add the priorities plugin to you yum installation and configure it to avoid problems with overwritten core packages.
upgrade to CentOS 6.4