CHECK_NRPE: Received 0 bytes from daemon -- but all test are


[root@tools nagios]# /usr/lib64/nagios/plugins/check_nrpe -H -p 5666 -c check_users
USERS OK - 2 users currently logged in |users=2;5;10;0

tools is the nagios monitoring server and is the serve being monitored.
As you can see the test is successful, however when the nrpe_check is run within nagios
I get this:
"CHECK_NRPE: Received 0 bytes from daemon. Check the remote server logs for error messages. "
in the status information column.
The tools server is a Fedora 5 and server 105 is RedHat 4 ES – We currently monitor 3 Rdhat Servers, 5 fedora servers and 5 windows servers. Only one has this symptom.

Any ideas why would help