I installed 2 ESX 3.5 Update 2 servers at the same time a few months ago. They are both DL380 G5s 14 GB RAM, 2 x Quad core processors and are attached to an MSA500.
ESX02 as I called it locks up once a week. The guests are in accessible and the Infrastructure client cannot connect to the serve. The only way I can get it back up is to connect to ILO and reboot it. The server is by no means stressed and has plenty of available resources.
I managed to get a look at what it says on the console when the above happens. It read
"kernel 2.4.21-57. Elvmnix on an i686 you probably have a hardware problem with your RAM chips. Please consult hardware error logs"
I booted the server off a diagnostic cd and ran a memory test and it gave the all clear, as usual
I am looking for a way to get the server to send out logs or see what is happening in the back-ground when this happens. I also have the HP Insight Management agents installed and the ILO doesn't have any errors when the server is locked up.