CentOS epel repository listed more than once

This error usually occurs when you have two repos with the same name. I think you may have named both the epel entries the same.

Try going into /etc/yum.repos.d

Look at both the epel files.

Check the name is different.

cd /etc/yum.repos.d
cat epel.*

Verify that they have different name.

The line you are interested in is:

name=SomeName

If they share the same name just change it so they are different.

Another possibility is that you have the same repo defined in different files. So do:

grep epel /etc/yum.repos.d/*

.. note the duplicates and rename/comment them out.