Error: Could not stat() command file

Problem:
When trying to "Re-schedule the next check of this service" and you get this error: Error: Could not stat() command file ‘/var/lib/nagios3/rw/nagios.cmd’!

Solution:

22:15:38 [root@pluto ~]# /etc/init.d/nagios3  stop
Stopping nagios3 monitoring daemon: nagios3
.
22:15:48 [root@pluto ~]# dpkg-statoverride --update --add nagios www-data 2710 /var/lib/nagios3/rw
22:15:58 [root@pluto ~]# dpkg-statoverride --update --add nagios nagios 751 /var/lib/nagios3
22:16:17 [root@pluto ~]# /etc/init.d/nagios3  start
Starting nagios3 monitoring daemon: nagios3.

Now the error is no more.

The solution above is for debian based but actually they are just fancy commands for a simple problem: permissions.
As stated in one debian bug report (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=571801), this is actually not a bug:

Nagios 3 is not configured to look for external commands in the default configuration as a security feature. To enable external commands, you need to allow the web server write access to the nagios command pipe. the simplest way of doing this is to set check_external_commands=1 in your nagios configuration, and then change the permissions in a way which will be maintained across package upgrades (otherwise dpkg will overwrite your permission changes).
[...]
This is done by intention and will not fixed.