Well it seems that QuickBooks Pro Desktop 2018 has issues when upgrading from QB 2016
First of all when upgrading to 2018 an error message 'QuickBooks could not update your company file' appears. One of the problems is that QB 2018 replaced your old QB app and you need that old 2016 version to take a fresh backup in the downlevel version. You can not just use a copy of the QB file, you actually need to do a Back-Up in 2016 first.
Once that is completed you can 'restore' the back up in 2018, convert the file to the new version and you'll be up and running.
So keep an old instance of QB 2016 on hand
Solved! Go to Solution.