[CentOS] Can't find repository for centosplus

    While trying to get my SD card reader to work with CentOS, it was 
recommended to me that I update to the centosplus kernel.
    I attempted to do so using yum, as was recommended, but I 
encountered the following error:

[root at localhost ~]# yum --enablerepo=centosplus update kernel
Repository update already added, not adding again
Error getting repository data for centosplus, repository not found

    So I checked the internet for answers, and it seemed that my 
/etc/yum.repos.d/CentOS-Base.repo file might not point to the right 
place. However, when I compared my centosplus entry in 
/etc/yum.repos.d/CentOS-Base.repo to examples on the net, it seemed to 
be correct:

#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus
baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0

    Why can I not access the repository and install centosplus?

Dave