Retention.dat - Permission Denied

Why would I get the following error when I restart the nagios service:

Starting nagios:touch: creating `/var/log/nagios/retention.dat’: Permission denied

The owner and group of the file are correct and the permissions are set to 600 which is set by default. I am running nagios as root, which I now is not recommended, but required to get a custom check to work correctly and the varous nagios.cfg variables are set correctly.

Any suggestions please? (It’s running on a RedHat Linux box.)

Thanks