ACL : all privileges set, but can't add files

[Claire D.]

Hello,
I manupulate the ACL, and I've got a problem, then I really don't anderstand
: 
to a user (/slide/users/toto) , I give all rights ( ALL ) . He can list
files, open files, BUT if he tries to add a file or create a folder, I
obtain a 403 error : forbidden : access denied  !
Is there somebody who has already obtained the type of problem?
Thank you,
Claire D.