Ldapadd returns Type or value exists

I'm trying to add groups to the my LDAP DB from a ldif file.
But I can not to do it becuase ldapadd returns ldap_add: Type or value exists (20).

$ ldapadd -x -W -v -D "cn=directory manager" -f ldap_groups.ldif
ldap_initialize( <DEFAULT> )
Enter LDAP Password: 
add gidNumber:
        3582
add objectClass:
        top
        groupofuniquenames
        posixgroup
add cn:
        group1
add uniqueMember:
        ... list of unique members here ...
adding new entry "cn=group1,ou=Groups,dc=mydomain,dc=com"
modify complete

add gidNumber:
        4912
add objectClass:
        top
        groupofuniquenames
        posixgroup
add cn:
        group3
add uniqueMember:
        ... list of unique members here ...
adding new entry "cn=group3,ou=Groups,dc=mydomain,dc=com"
ldap_add: Type or value exists (20)

In result I have a successfully added part of groups untill group3.

ldapsearch has not found the group3:

$ ldapsearch -x -b "dc=mydomain,dc=com" |grep group3
$ 

Could you help me?