Users in my LDAP database have trouble changing passwords.

$ passwd
Changing password for user XXX.
Enter login(LDAP) password: 
New password: 
Retype new password: 
LDAP password information update failed: Insufficient access
passwd: Authentication token manipulation error

In /var/log/message, I have:
passwd: pam_ldap: ldap_modify_s Insufficient access

In slapd.conf on the server, I have the following:

database bdb
suffix dc=mydomain,dc=fr
checkpoint      1024 15
rootdn cn=Manager,dc=mydomain,dc=fr
rootpw {SSHA}XXXXX

access to attrs=userPassword
  by self write
  by * none

access to dn.subtree="dc=mydomain,dc=fr"
  by dn="cn=Manager,dc=mydomain,dc=fr" write
  by self write
  by * read

Any idea what is wrong?
Thanks in advance.

F.