"Cannot Save because Project is Corrupted" error message after upgrading to SpectraLayers Pro 9

This is the very first time I get the error message
“Cannot Save because Project is Corrupted”
I had unmixed stems on 2 songs in SpectraLayers Pro 9, and then dragged the stems to the Project Window.
I pressed Undo and then Redo in both SpectraLayers Pro 9 and Nuendo 12.0.30.
After that the Project became Corrupted.

Windows 10, latest updates.

Sounds like a Nuendo issue given the description.