Hi All
Thank you for all your tips !

I missed this thread due to illness, but promtply checked my KPC and it was not working anymore. Downloaded new version, but it can't read any of my AMZ books. Tried to delete books, re-download, but no joy. Kind of stuck here.
Will experiment some more, and report back
Cheers Per,
Edit: Don't know why, but I have to check each downloaded AMZ book. IF it fails I have to remove it from "MY Device" ie. K4PC, then go to Archived Items, double click the book and it downloads, and that book is OK.
Edit 2: Only got that far after de-/re-registering K4PC
Edit 3: NOW totally confused. Apparently Amazon had some sort of outage, because now syncing seems to work for all my books. Ie. double click the book in K4PC an a "new" one is downloaded.