Thank you very much for your answer Monica !
But what do you mean by this ? How could it be the cause ?
I tried different way of "backing up" today and it seems I have some kind of a debug message after all ! (Sorry I didn't notice it earlier...)
When I tried to back up only the Nanogong exercices (no groups, no users data, etc.), I have exactly this same message :
◦ NanoGong "Prononcer"
• Could not restore modules!
• Création des définitions des rôles
• Création des attributions de rôles et des dérogations pour les cours
• Création des attributions de rôles et des dérogations pour les modules
• Création des attributions de rôles et des dérogations pour les blocs
• Création des attributions de rôles et des dérogations pour les utilisateurs
• . . . . . . . . . . . . . . . . . . . .
• . . . . . . . . . . . .
• Notice: Trying to get property of non-object in /Applications/MAMP/htdocs/moodle19/backup/restorelib.php on line 9378
• Closing the Restorelog.html file.
An error has occurred and the restore could not be completed!
Stack trace:
• line 1664 of lib/deprecatedlib.php: call to debugging()
• line 69 of backup/restore_execute.html: call to error()
• line 174 of backup/restore.php: call to include_once()
The line 9378 of restorelib.php is : $assignment->roleid = $role->new_id; // restored new role id
So my Nanogong problem would come from this line ? Moodle couldn't give a new role id to my Nanogong assignments ?
Thank you for your help !