i am following this link with an aim to create custom CentOS ISO with some extra packages downloaded from internet (say ABCD.rpm). https://wikis.uit.tufts.edu/confluence/dis
You have to add '-joliet-long' option to mkisofs. These file name under the /repodata is too long.
I was running into the same issue. It is working fine after using the following command to create ISO.
mkisofs -r -N -L -d -J -T -joliet-long -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -V RHEL6.5 -boot-load-size 4 -boot-info-table -o RHEL6.5-20131111.0-Server-x86_64-DVD1_new3.iso RHEL6.5-20131111.0-Server-x86_64-DVD1_new
You have to re-create the comps.xml for any new added package.
cd <your_working_path>/isolinux
createrepo -u "media://`head -1 .discinfo`" -g <your_working_path>/comps.xml .