http://wiki.centos.org/Manuals/ReleaseNotes/CentOS6.3 (Section 4. Major Changes) Matahari is now obsoleted, but in 6.1, had a dependency on qpid-cpp-server and qpid-cpp-client which wanted updates. A quick Google shows many others seeing this problem. I think if you run yum with the --obsoletes flag you may get more information. IMHO you need a human to decide when/if to remove the obsoleted packages and proceed with the update.