Nagios-4.2.4 got pushed to epel stable this week. I thought I had put it in to be more weeks and a higher karma but something I did later screwed that up.
As shown in https://bugzilla.redhat.com/show_bug.cgi?id=1427895 this breaks existing installs. I had hoped this was fixed and found from other testing but clearly I missed a lot of cases. I am working on what can be done to fix this, but at the moment my apologies.
epel-devel@lists.fedoraproject.org