Hope this helps somebody:
After transitioning to iLok and updating VE Pro from 7.0.1120 to 7.1.1298, I was unable to open any of my VESP64 projects, and unable to import a single instance from any of those project to a new project. Tried everything suggested on various posts uninstalled/reinstalled around a dozen combinations of old/new versions of VE Pro 7, manually and via Vienna Assistant. None of it worked, just kept getting the dreaded "instance invalid" messages. For no logical reason whatsoever I decided to open the eLicenser Control Center (which should be redundant after having migrated to iLok, right?) on my server computer and check for updates. As soon as I updated eLicenser Control Center from v 6.11 to v6.12.8.3308, I was able to open every single project/instance!
So if anyone is having issues with invalid VE Pro 7 projects/instances after migrating to iLok, try updating eLicenser Control Center to the latest version (currently v6.12.8.3308) and see if it works for you too. Make sure you have the eLicenser dongle connected to your server computer when you try to open the FIRST project created in VE Pro 7.0.1120. I removed the dongle once I was able to open the first project, and was able to open all my other projects (each around 15-20 instances, with each instance having 10-16 instruments, i.e. not exactly small projects) without the dongle connected.