Which ESXi image are you using for the upgrade (VMware or HP OEM)?
You can find the the links to the HP OEM images at http://www.hp.com/go/esxidownload
Btw. please ensure that you update the "esx-base" vib to the latest available after installing the HP image (see e.g. https://esxi-patches.v-front.de/ESXi-6.0.0.html)
André