Check all cable connections and the connection of a reliable power supply, and then try again.
In all upgrades a text log file is created, this file can be emailed to your local VBOX agent to help diagnose any upgrade problems.
In some cases the upgrade process may fail towards the end, during the EEPROM programming stage. This can be overlooked, as the important stage is the programming of the Flash and this was probably successful. If the upgrade failed during the EEPROM stage then it will only mean that your basic settings like velocity units will need to be manually reset.
If problems persist, please raise a support ticket for further help.