Probably do as asked, reassign the interfaces to get yourself access to the webgui again. Make note of what interface names come along em0 igb1 ix2 re3 or others?
-make sure you have a backup of the config from before upgrade as soon as possible(hopefully you made a backup before starting the upgrade) otherwise copy the /cf/conf/backup files somewhere asap.
it might be that one of the interfaces got recognized under a new name.. figure out which is which.
Assuming all nics are still recognized but some names are different than before, then take a old/good backup config.xml and restore it through the webgui, it should then also ask to reassign the interfaces. or edit the config manually before restoring it by putting the correct interface-names.. That should hopefully get you running again..