I've installed and got Nagios to show the localhost and another windows computer. The web interface worked and the services properly showed up. After I got that working I wanted to set up email notifications. I installed mailx and configured postfix to relay to a local M$ exchange server. Now that the notifications work, the web interface no longer works. Previously when I would go to 10.1.1.10 it would say that it didn't exist or something similar and now it says "10.1.1.10 is currently unable to handle this request." And previously when I would go to 10.1.1.10/nagios it would come up correctly and now it says "The server encountered an internal error or misconfiguration and was unable to complete your request." The weird thing is, is that I'm getting email notifications now saying that localhost is down.

Info: (No output on stdout) stderr: execvp(/check_ping, ...) failed. errno is 2: No such file or directory

Heres my nagios.log after a reboot

[1490635800] Nagios 4.2.4 starting... (PID=1337)
[1490635800] Local time is Mon Mar 27 12:30:00 CDT 2017
[1490635800] LOG VERSION: 2.0
[1490635800] qh: Socket '/usr/local/nagios/var/rw/nagios.qh' successfully initialized
[1490635800] qh: core query handler registered
[1490635800] nerd: Channel hostchecks registered successfully
[1490635800] nerd: Channel servicechecks registered successfully
[1490635800] nerd: Channel opathchecks registered successfully
[1490635800] nerd: Fully initialized and ready to rock!
[1490635800] wproc: Successfully registered manager as @wproc with query handler
[1490635800] wproc: Registry request: name=Core Worker 1345;pid=1345
[1490635800] wproc: Registry request: name=Core Worker 1343;pid=1343
[1490635800] wproc: Registry request: name=Core Worker 1344;pid=1344
[1490635800] wproc: Registry request: name=Core Worker 1342;pid=1342
[1490635800] Successfully launched command file worker with pid 1366

I've tried restarting the nagios service and httpd as well. plz help
CentOS7
Linux version 3.10.0-514.10.2.el7.x86_64
Nagios 4.2.4

SElinux disabled
firewall is off

The problem I had was clearly spelled out in the httpd error log. The htpasswd.users file didn't have read permissions for apache.