We learned today of a particular set of circumstances which, when updating to Update 1, can lead to PSODs (purple screens). 3rd party agents are a key component of this problem.

To avoid this potentially nasty problem please read the following Knowledgebase article for details:

Upgrading ESX 4.0 to 4.0 U1 using Update Manager fails or times out and rebooting host results in a purple diagnostic screen (1016070)

Symptoms

When attempting to upgrade ESX 4.0 to ESX 4.0 Update 1, you may experience the following symptoms:

• Update manager (VUM) upgrade operation fails or times out at 33%.
• Upon reboot, the host that was being upgraded displays a purple diagnostic screen with the following error:
  COS Panic: Int3 @ mp_register_ioapic

See Also KB1016070