That's a pretty common problem
You've had wrong file permissions set for the check_icmp script (located in libexec directory).
This one is beeing used for hosts availability checking (in standard configuration).
It needs the "set user or group ID on execution" bit set for the owner of the file and root:root ownership to work properly
And that's it
By the way - the same file permissions are required for the check_dhcp script
Take care
Michalux