I didn't use to get it, I have already uploaded like 11 users
Does anyone know what this is about?
Switch on Debugging (<< that's a link). Do it again. Hopefully you should see some additional messages. Let us know what they are.
We're hoping this will give a clue to the underlying problem.
"id_alumno_pts" - missing default value in the SQL table "mdl_user" or value sent on submit
There's no such field as id_alumno_pts in the mdl_user table. Well, there isn't in unmodified Moodle anyway.
So.... how did that field get there on your installation?
^ this
did you manually modify the moodle database schema to implement something (such as a point system?) - specifically, adding a column in the mdl_users table?
Because, with respect, that's a really bad idea.