Creating basic Register (username/login/password)

[eluser]jvicab[/eluser]
No, that is not right. You cannot name your consturctor like this. The constructor name is always __construct() regardless the name of the class, and the parent constructor should be called like parent::__construct().
Your problem is caused by one of two things: or you are not loading the model or you are but CI cannot link it based on the naming convention. Try to code your constructors (only if you need to put some code on it) the way I suggested (for controllers and models and any other class you intyent to extend):

class Somename extends Parentclass
{
function __construct()
{
parent::__construct();
// your code here
}
}