After a number of issues were found with update 1 in relationship with HP management agents VMware have rereleased a fixed version of the update called update 1a.
The symptoms of the problem are described in the KB article as
When attempting to upgrade ESX 4.0 to ESX 4.0 Update 1 (U1), you may experience these symptoms:
- Upgrade operation may fail or hang and can result in an incomplete installation
- Upon reboot, the host that was being upgraded may be left in an inconsistent state and may display a purple diagnostic screen with the following error:
COS Panic: Int3 @ mp_register_ioapic
During the ESX 4.0 Update installation a process checks for running agents and stops them before proceeding.
Full information about this issue can be found in the KB here >> http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1016070
Update 1a is available from update manager and the download site now