Tnak you for your answer.
The cluster has worked well until a switch to witch the servers were connected has failled and was replaced. After that the when I had connected to vSphere two servers had exited from cluster.
From VMware KB: Troubleshooting VMware High Availability (HA) in vSphere all steps seem to be right for me.
I have tryed this VMware KB: Recreating a VMware High Availability Cluster in vSphere with one server ( and on the same cluster ) but when I add it back to cluster I receive the error message "Cannot complete configuration of the HA agent on the host. Other HA configuration error".