During the upgrade process from 5.5 to 6.5 (using the ISO method), I ran into the following error:
CONFLICTING_VIBS ERROR: Vibs on the host are conflicting with vibs in metadata. Remove the conflicting VIBs or use Image Builder to create a custom upgrade ISO providing newer versions of the conflicting vibs.
The vib listed as the problem was HUAWEI_bootbank_hio_22.214.171.124-1OEM.550.0.1331820
The next step was to cancel the upgrade process and reboot back into 5.5. Once you are back into ESXi, bring up the console and list all installed vibs by using the following command (pipe in the more command to break the list into pages):
esxcli software vib list | more
In this particular case the problematic vib was called hio
To remove it, initiate the following command:
esxcli software vib remove --vibname hio
Once it completes, reboot for the removal to cleanly take effect. Then reboot again and boot off your ISO installer to restart the ESXi upgrade process.