firing up example blogpost gets me now an Attribute error

[JC]

'Blogpost' object has no attribute 'format'

Request Method: GET
Request URL: http://localhost:8000/api/posts/?format=json
Django Version:1.3.1
Exception Type: AttributeError

Exception Value: 'Blogpost' object has no attribute 'format'
Exception Location: C:\dev\django-piston\examples\blogserver\../../
piston\emitters.py in <genexpr>, line 244

Any ideas? I was just trying to follow the example I just downloaded.
No modifications other than the admin fix in the urls.py

thanks