May 14 16:33:17 localhost nagios: Warning: Attempting to execute the command "/usr/bin/printf "%b" "***** Nagios *****\n\nNotification Type: PROBLEM\n\nService: CPU Load\nHost: remotehost.domain.com\nAddress: xx.xx.xx.xxx\nState: CRITICAL\n\nDate/Time: Mon May 14 16:33:17 CEST 2007\n\nAdditional Info:\n\nConnection refused by host" | /bin/mail -s "** PROBLEM Service Alert: remotehost.domain.com/CPU Load is CRITICAL **" magnet@somewhere.com" resulted in a return code of 127. Make sure the script or binary you are trying to execute actually exists..