I can't save my project, I've got this message (capture)

Hello Maud,

I'm sorry to hear about the issue you are having with saving your file.  This support article covers best practices in saving your files locally:

Storyline: Create, Edit, and Publish Courses on Your Local Hard Drive

You can also try to import the saved version of the slides into a new project.

Otherwise, you may want to reach out to our support engineers here to help review this issue.