Hi, I'm new to Krita.
I tried Krita on my laptop. New Asus laptop mid-range with Windows10.

I open an existing file and then try to save it (under a different name)
This does not work. Get the following message:
C:/Temporary/filename.jpg could not be saved.
Reason: Could not open the file for writing. Reason: The file could not be opened.

What's wrong?

Johan

You probably don't have the rights to save in that location. Save in your Pictures folder instead.