Right now, I am working on modifying this extension to be scalable by using memcached as storage for OAuth Token info instead of local cache.
So I do not have enough time and environment to work on the problem you have.
But I will get back to you soon after the modification is done.
In the meantime, could you check a few things for me?
Right after provider.retrieveAccessToken, could you put these lines below?It will give you AccessToken and TokenSecret you have to use to get access to protected resources.