Comment 17 for bug 436544

If you have changed the ownership of /usr/lib/cups/filter and /usr/lib/cups/backend to root and the group to root, and are still getting this message, you have a SElinux problem. Change SElinux from enforcing to permissive as explained here:
http://www.crypt.gen.nz/selinux/disable_selinux.html

Good luck!