newbie question

[srgqwerty <srgqwerty@telefonica.net>]

I pretend to do the following:

dc=tux,dc=org is the root
o=tux,dc=tux,dc=org is CHILD OF dc=tux,dc=org
ou=sels,o=tux,dc=tux,dc=org is CHILD OF o=tux,dc=tux,dc=org
ou=mai,o=tux,dc=tux,dc=org is CHILD OF o=tux,dc=tux,dc=org

In other words, "sels" and "mai" are both in the same level and BOTH OF 
THEM have a parent O=TUX

I have the following struct.ldif file:

# ----- BEGIN OF LDIFF FILE -----
# Entry for create o=tux,dc=tux,dc=org
dn: dc=tux,dc=org
objectClass: organization
o: tux
                                                                                                                                             

# Entry for create ou=sels,o=tux,dc=tux,dc=org
dn: o=tux,dc=tux,dc=org
objectClass: organizationalunit
ou: sels
                                                                                                                                             

# Entry for create ou=mai,o=tux,dc=tux,dc=org
dn: o=tux,dc=tux,dc=org
objectClass: organizationalunit
ou: mai
# ----- END OF LDIFF FILE -----

But when I run the following commands an error occur (ldap_add: Already 
exists) and the entry ou=mai,o=tux,dc=tux,dc=org is not added.

[root@this tux_entries]# ldapadd -x -D 'cn=Manager,dc=advr,dc=org' -w 
blablabla -f struct.ldif
adding new entry "dc=tux,dc=org"

adding new entry "o=tux,dc=tux,dc=org"

adding new entry "o=tux,dc=tux,dc=org"
ldap_add: Already exists

ldif_record() = 68

[root@this tux_entries]# ldapsearch -b 'dc=tux,dc=org' 'objectclass=*'
dc=tux,dc=org
objectClass=organization
o=tux

o=tux,dc=tux,dc=org
objectClass=organizationalunit
ou=sels
2 matches
[root@fwall1 advr_entries]#

What am I doing wrong?

Thanks