During the last few weeks, I have a problem in our VMWARE ESX cluster (Rel.3.5, build 207095): 1 of the 9 servers appears as disconnected in the vSphere client of our vCenter Server (both: Rel.4.0.0, build 258672), while it seems to have a normal operation (the ESX Server console is displayed on the system's screen, it accepts login connections and any Linux command via SSH and it seems to have access to all the VMFS volumes on the shared storage engines). Whenever I reboot that server, it seems to be connected to the cluster ("Connected" state and "Normal" status) for a few seconds (less than 1 minute) and then goes into "Not responding" state. Same thing happens whenever I re-connect that server to the cluster (by right-clicking on its entity in the vSphere client and selecting "Reconnect"). Restarting the VMWARE management services via command-line on the server ("service mgmt-vmware restart" and "service vmware-vpxa restart") did not resolve the problem.
Advice is always welcome - thanks in advance.