Can not add a subscription

I have installed membership Premium, followed the manual to the word, but when I go to add a subscription (again following the manual to the word) when I click 'Add' at the bottom it returns to the subscription page with a message

Subscription not added.

Anyone have any idea why this might be happening

I am using Chrome and Safari both with same errors
Wordpress single install version 3.3.2

Any help gratefully appreciated.

Dermot