Try this if you are getting that message. I know read the manuel!!!!)
8) Modify SELinux Settings
Fedora ships with SELinux (Security Enhanced Linu:evil: installed and in Enforcing mode by default. This can result in "Internal Server Error" messages when you attempt to access the Nagios CGIs.
See if SELinux is in Enforcing mode.
Put SELinux into Permissive mode.
To make this change permanent, you'll have to modify the settings in /etc/selinux/config and reboot.
Instead of disabling SELinux or setting it to permissive mode, you can use the following command to run the CGIs under SELinux enforcing/targeted mode:
chcon -R -t httpd_sys_content_t /usr/local/nagios/sbin/
chcon -R -t httpd_sys_content_t /usr/local/nagios/share/
For information on running the Nagios CGIs under Enforcing mode with a targeted policy, visit the NagiosCommunity.org wiki at nagioscommunity.org/wiki.
nagios.sourceforge.net/docs/3_0/ ... edora.html