how did you install fusion ?
-- from the instructions on the wiki --
also fusion has no cent6 " el6" and almost no cent 5 - el5
rpmforge is the main
rpmforge-extras IS INCOMPATIBLE with RHN and cent and SL base install
-- fallow ALL warnings about the NEED for "yum-Priorities" and possibly " yum-ProtectBase"
"yum-Priorities" IS needed and you NEED to configure it