VMWare ESX 4 Error

Does anyone know how to fix this alarm, or what the cause may be:

Stateless event alarm  
Alarm Definition:
([Event alarm expression: Host error] OR [Event alarm expression: Host warning])
Agent can't send heartbeats.msg size: 66, sendto() returned: Operation not permitted
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Paul SolovyovskySenior IT AdvisorCommented:
Try rebooting vCenter server
Jack_son_Author Commented:
Rebooted, but still getting the alert
Has the been  firewall changes on the hosts?

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