by Iñaki Arenaza.
Hi,
the thing is you need to set a password for the user, because Moodle will check the password in the database when you don't use an external authentication system (like LDAP).
You can probably set the same password for all the users in your case. You simply need to copy the password field from the admin user to all the other users (I assume you know the admin password )
Saludos. Iñaki.