Restoring PC backup to new Mac fails

Hi, I’m new to eM Client and have compounded that by switching from a Windows 10 PC to a Mac Mini. Both are running eM Client.
As suggested by the eM Web site, to migrate over I updated both machines to the latest version software, then did a manual backup onto a USB. All good so far.
Started the Mac copy of eM and skipped the set-up process as suggested, then went to the file-restore and pointed it to the USB backup. All seemed good until the restore was done and eM attempted to restart!
Screenshot 2021-05-15 at 19.00.45
It first demanded to be updated and then couldn’t find the update, throwing a “(404) the specified blob does not exist” error.
Now eM will not start without an update it cannot find and I can’t get rid of the restored backup.
Anyone have a solution please? I have bought licenses for eM.