django-dbindexer error: name must be an instance of basestring

I'm using Django-nonrel from All Buttons Pressed, and trying to imple开发者_Go百科ment django-dbindexer. I can connect to MongoDB, create, update and delete documents.

However, when I tried implementing django-dbindexer, I get the following exception:

Caught ImproperlyConfigured while rendering: name must be an instance of basestring

Here's my model, settings and dbindexes:

#settings.py
DATABASES = {
    'default': {
        'ENGINE': 'django_mongodb_engine',
        'NAME': 'test',
        'USER': '',
        'PASSWORD': '',
        'HOST': 'localhost',
        'PORT': 27017,
    }
}

DATABASES['native'] = DATABASES['default']
DATABASES['default'] = {'ENGINE': 'dbindexer', 'TARGET': 'native'}
AUTOLOAD_SITECONF = 'dbindexes'

MIDDLWARE_CLASSES = (
    'autoload.middleware.AutoloadMiddleware',
    ...
)

INSTALLED_APPS = (
    ...
    'blog',
    'autoload',
    'dbindexer',
)

#blog/models.py
from django.db import models
from djangotoolbox.fields import ListField

class Post(models.Model):
    title = models.CharField(max_length=100)
    text = models.TextField()
    tags = ListField(blank=True)
    comments = ListField(blank=True)

    def __unicode__(self):
        return self.title

#base dbindexes.py
from dbindexer import autodiscover

autodiscover()

#blog/dbindexes.py
from blog.models import Post
from dbindexer.api import register_index

register_index(Post, {'title' : 'iexact'})

Can anyone see what I'm doing wrong? Many thanks in advance!

[Update] Here's the full traceback: http://pastie.org/2346423