Hello, and first : Merry chrismas!

So, i am not developper and am discovering j-cook.
I have done a first project to understand : test 1 and a second : elevage retrievers to really work.
Yesterday evening i came back to work on elevage retrievers, first i began to use sandbox to see what i had done before.
At that moment : on step : backup data set , i had a red "!" and couldn't go further.
I went to have a look to my dataset => no snapshots. There was a few ones before.
Thinking, i did a mistake i have destroyer a part of the tables i needed : those with a FK, the pages...
Always the same.

So i went to watch in my first project : test1.
Sandbox => same problem on backup data set, but all my snapshots in dataset are there.

Can you tell me what tot do?
All the best GillesT