VMware KB1016262 – vCenter Agent Install Fails on ESXi 4 Host
VMware just posted an alert on this for ESXi 4 Hosts managed by either vCenter 4 or 4 Update 1. If you remove and re-add the Host to vCenter, or upgrade vCenter to Update 1 you may experience this issue.
At this time, there is no official fix, however it appears a reboot should fix the issue but with the Host disconnected from vCenter; vMotion is not an option and the disconnect may trigger HA, but I would hope that you have placed this host into Maintenance Mode prior to disconnecting from vCenter…right? Also, HA should have been disabled prior to your Update 1 patch…you did that as well, right?
Read the official VMware Alert here.
VMware KB1016262 – vCenter Agent Install Fails on ESXi 4 Host