Google App Engine: using generate_records with the bulkloader

Question

I'm using Python 2.5 locally and GAE 1.5. I'm trying to load data which is not is CSV format. Here's a simplified model which reflects what I get with a more complex real life issue:

class Thing(db.Model): 
    name = db.StringProperty() 

class ThingLoader(bulkloader.Loader): 
    elements = [ 
        ('name', str) 
    ] 
    def __init__(self): 
        bulkloader.Loader.__init__(self, 'Thing', self.elements) 

    def generate_records(self, filename): 
        records = load_records_from_some_datasource() 
        for record in records: 
            yield [ 
                record['name'] 
            ] 

loaders = [ThingLoader]

When I try to bulkload this (both locally or to google) I get: InternalError: Put accepted 10 entities but returned 0 keys. I can't work out why the datastore will not allocate keys, I have even tried writing a generate_keys of my own for the loader.

Here's my command line call:

python "C:\Program Files\Google\google_appengine\\appcfg.py" upload_data --url=http://localhost:8080/remote_api --config_file=data_api.py --filename=raw.dat --kind=Thing --log_file=logfile.log --email=col.wilson.email .

Any ideas what I should do?