I'm calling a web API exposed by TheyWorkForYou (TWFI). http://www.theyworkforyou.com/api/

I'm using the Python bindings provided by twfython: http://code.google.com/p/twfython/

I wrote some code to call this API a few months ago, at which time it worked fine. But now I dig it out to run it again, no matter what query I ask of the API, it always returns '{}' (an empty dictionary). For example the following code, which should return a list of all MPs:

from twfy import TWFY
API_KEY = 'XXXXXXXXXXXXXXXXXXXXXX'
twfy = TWFY.TWFY(API_KEY)
print twfy.api.getMPs(output='js')

Am I being really dumb? What else should I check?