Cannot write to a specific tvg element

I am working on a file and keep getting the same repeated problem. When I try and save my file, I get the following error:
“Cannot write (pathname.tng)”

Can anybody help with this. I read another post which identified a problem as read/write privileges not assigned to folders, but I have checked each element in each folder and I have privileges for each of them. I really don’t want to lose the hours of work I have put into this particular frame on this particular layer. Any suggestions?

Contact support to have a look at the project and it’s location on your computer.
If you have a Mac, see if there’s already a file there named similarly except for
using (perhaps?) and upper-case letter instead of a lower-case one.

Try making a template of the element, deleting if from the project and
saving. If you drag the template back into the scene. Are you now able
to save?