J'ai fait réparer les authorisations directement sans passer par la case vérifier :
Determining correct file permissions.
We are using special permissions for the file or directory ./Library/ColorSync/Profiles/Displays. New permissions are 16893
We are using special permissions for the file or directory ./Library/ColorSync/Profiles. New permissions are 16893
Permissions differ on ./Library/Preferences/com.apple.dockfixup.plist, should be -rw-rw-r-- , they are -rw-r--r--
Owner and group corrected on ./Library/Preferences/com.apple.dockfixup.plist
Permissions corrected on ./Library/Preferences/com.apple.dockfixup.plist
We are using special permissions for the file or directory ./System/Library/Filesystems/cd9660.fs/cd9660.util. New permissions are 33261
Permissions differ on ./private/etc/slpsa.conf, should be -rwxr-xr-x , they are -rw-r--r--
Owner and group corrected on ./private/etc/slpsa.conf
Permissions corrected on ./private/etc/slpsa.conf
We are using a special uid for the file or directory ./private/var/at/jobs. New uid is 1
We are using a special uid for the file or directory ./private/var/at/spool. New uid is 1
Group differs on ./private/var/log/install.log, should be 80, group is 0
Owner and group corrected on ./private/var/log/install.log
Permissions corrected on ./private/var/log/install.log
The privileges have been verified or repaired on the selected volume
Réparation des autorisations terminée
La réinstalle : réinstalle sans formatage (je me souviens qu'il y avait 2 cases de cochées au départ dans les choix et qu'il fallait cocher la case formatage (que je n'ai donc pas cocher), il ne m'a par contre pas demandé le 3éme CD