Pages and Preview -  saving/writing on files

The problem does not occur with “Golden Gate”, but much earlier.

It affects files on both external SanDisc volumes and on the Mac HD.

When closing/saving Pages documents or images in Preview:

“The document could not be autosaved.

Your most recent changes might be lost.”

“The document "Screenshot….. .png" is on a volume that does not support permanent version storage.

Your changes have been saved and you will not be able to access older versions of this document once you close it. To undo your changes, click Revert.”

“The document “……..  pages” is on a volume that does not support permanent version storage.

You will not be able to access older versions of this document once you close it.

Don't ask again”

Or even :

“You don't own the file “……….. pages” and don't have permission to write to it.

You can duplicate this document and edit the duplicate. Only the duplicate will include your changes.

Cancel  Duplicate

Whereas the file info reads: 

Sharing & Permissions: You can read and write

It’s not a storage problem, there’s enough disc space. I’m the only user, none of the files are shared.