Hey Nina,
Sorry, I am bit late to anawring so you might already have found a solution to your problem.
We will need a lot more dtails than the screen shot, please:
Like Davinci version number?
Are you PC or Mac?
Have you previously been able to back up the project, to the same location?
And so forth.
If you have found a solution, please feel free to share so other users with the same problem, can find it.
Atb
Mads