Right. We have changed the underlying architecture in R80.x compared to the older versions. That's why you might need to make some changes to configuration before upgrade is allowed.
The same tgz-packet with the migrate-script contains another script called pre_upgrade_verifier. Run that script to get a report of possible problems and how to change them. Syntax is something like ./pre_upgrade_verifier -c R77 -t R80
There are three categories of messages in the PUV-report:
ERROR: Must be fixed before the upgrade can take place
WARNING: Recommended to be fixed before or after the upgrade
INFORMATION: No need for action. Just good to know info.
After fixing the issues, run migrate export again.
Also please review Release Notes and Installation and Upgrade Guide for the relevant version.