Both system.cpu.load and system.cpu.util items are unsupported
[root@monitoring ~]# ./zabbix_get -s citadel -k system.uname
Windows CITADEL 6.0.6002 Windows Server 2008 Service Pack 2 AMD-64
[root@monitoring ~]# ./zabbix_get -s citadel -k system.cpu.util[0,,]
Collector is not started!
Forum thread about this topic
http://www.zabbix.org/forum/showthread.php?t=13132