What did you see now before the error dialog came?
Normally, it goes in this sequence, so let me know until which point it reached:
1. You click to save
2. A “Saving project…” dialog comes up, and now it also shows “(Exporting project files)”
3. Next the second part should say “(Sending files to server)”
4. Next it might also also show “(Uploading progress)”
Do you remember until which point it reached?
There is no sure way to say you will be able to save, but I also fixed an issue of the client hanging when the save failed, so hopefully you can try multiple times.
Maybe try this:
1. Log out first (log out button, the same place where the project can be saved)
2. Log in again.
3. Save your project.
I sure hope you don’t lose your progress anymore Aura :(.