Hi,
Sorry I did not follow up on this post.
I finally manged to convert all dbs to ODS52.
I used these documents :
"How do you upgrade the database ODS?" from Keysolutions.com
"Notes Client upgrade and ODS upgrade" from shrinilotustech.blogspot.fr
and "New ODS in 9.0.1 - ODS 52" from Arkadiusz Smakowski and Ulrich Krause who wrote "NSF_UpgradeODS is a Notes Client only feature and not applicable to Domino Server. (Documentation / Admin Help is wrong )".
Thanks to all contributors.
Jean-Pierre