When patching ESX Hosts with iSCSI attached SAN’s it’s possible you encounter the following event when starting a VM:
“A general system error occured: The system returned an error. Communication with the virtual machine may have been interrupted.”
This is caused by the fact that the “Software iSCSI Client” isn’t enabled on the ESX firewall. November the 15th VMware released a couple of patches which addressed a bug. This bug made it possible to connect via the iSCSI software initiator without enabling the service on the ESX firewall. To open up the port open a console session to the ESX host and type “esxcfg-firewall -e swISCSIClient” or enable it via VirtualCenter “Configuration -> Security Profile -> Properties -> Check Software iSCSI Client”.