Re: upgrade fro ESXi 4.0U2 -> 4.1 didn't work?
If 4.1 is correctly installed to what gets mounted as /altbookbank you can
1) Create a file in /altbootbank so that you can identify it later.
2) Boot ESXi with a Linux live CD and mount partition 1 and 2. See the example here - http://www.vm-help.com/esx/esx3i/disabl ... tartup.php
3) Once you have figured out which partition is /altbootbank - edit boot.cfg to add the option.
4) Reboot and at the initial ESXi boot menu press shift+R to revert back to the prior system image (which in this case would be the 4.1 install).
You could also try this
Boot ESXi, use the revert option and pass the vmkernel option as described in the prior link. I don't know if you can do both at the same time though.