Thanks for your clues! That is working after:
1.- "cifs setup" -> option (4) etc/passwd and/or NIS/LDAP authentication
2.- Filer: "useradmin user add User1 -g Guests"
3.- Fix a password for "User1" with passwd command
4.- Assign "Full Access" to User1 in share access
5.- Adding "*\User1 => root" in usermaps file in /etc
6.- Mounting the cifs share from linux client as:
mount -t cifs //"filer ip"/"ShareToMap" /"LocalMountPoint" -o user="User1"
Best regards,