I see an error while using NConf interface in Generate Nagios config

Error accessing or executing Nagios / Icinga binary '/usr/sbin/nagios'.
Cannot run the mandatory syntax check.

I checked Apache Error_log and it says:

sh: /usr/sbin/nagios: Permission denied

I tried changing permissions and ownership but no change.

How can I fix this?

Edit:

ls -l /usr/sbin/nagios

-rwxrwxrwx. 1 apache apache 644184 Jul 2 02:10 /usr/sbin/nagios

ps -ef | egrep 'httpd|apache'

root      4175     1  0 10:50 ?        00:00:00 /usr/sbin/httpd
apache    4177  4175  0 10:50 ?        00:00:00 /usr/sbin/httpd
apache    4178  4175  0 10:50 ?        00:00:00 /usr/sbin/httpd
apache    4179  4175  0 10:50 ?        00:00:00 /usr/sbin/httpd
apache    4180  4175  0 10:50 ?        00:00:00 /usr/sbin/httpd
apache    4181  4175  0 10:50 ?        00:00:00 /usr/sbin/httpd
apache    4182  4175  0 10:50 ?        00:00:00 /usr/sbin/httpd
apache    4183  4175  0 10:50 ?        00:00:00 /usr/sbin/httpd
apache    4184  4175  0 10:50 ?        00:00:00 /usr/sbin/httpd
apache    4559  4175  0 11:31 ?        00:00:00 /usr/sbin/httpd
root      4888  4854  0 12:26 pts/1    00:00:00 egrep httpd|apache