NoReverseMatch error in Django 1.8

Using the Django admin to add users I get the error: NoReverseMatch at /admin/usuarios/user/add/ Reverse for 'usuarios_user_change' with arguments '(u'',)' and keyword arguments '{}' not found. 1 pattern(s) tried: [u'admin/usuarios/user/(.+)/$'].

I'm using AbastractBaseUser and UserAdmin

All I have for the admin in URLConf is

url(r'^admin/',include(admin.site.urls))