Have you tried running yum repo-regen (or was it regen-repo?) on the client?
Can you run `ftp master` from the client's command line successfully?
Have you tried re-running createrepo (mrepo)
what's the output of yum list-repos (list-repo? repo-list? It's been a couple year's since I managed an RPM package server) on both the client and server.
Also the output of rubygems.noarch ...el6 makes me think that's from EPEL and not your local repo, but maybe you're just running a mirror and it is