Today I had some HA errors on our environment. In ESX 3.5 update 3 a lot has changed in the Service Console for HA. The reconfigure HA option didn't work for me and the error stayed. So I've resolved this issue by renaming the FT_HOSTS file in '/etc/opt/vmware/aam' and issued a 'Reconfigure for VMware HA'. Worked like a charm!

By the way, XTRAVirt has written an excellent pdf about HA and how to troubleshoot. Check it out here: hlink