Project is not compatible with current version - even so it was saved an hour ago
I am using a iMac with OS X 10.14.1 (18B75) (= Mojave).
Even so I do not know whether that is part of the problem, I will try to describe it here.
Since a while I experience situations, that I save a project with Adobe Premiere Elements 14 and an hour later I cannot open it anymore.
The software tells me: "This project is not compatible with the current version of Premiere Elements". Even the autosaved project file would refuse to work for me with the same (damned) message.
Sometimes it would help, that I opened a backed up project file (several month old) to work on the project again.
Any hints or help from anybody??
Message screen (in German):

