Google Contacts oAuth in asp.net /C#

Question

I'm trying to use oAuth to access google contacts. I'm using the example source code used in http://github.com/bittercoder/DevDefined.OAuth

I get an error saying the token is invalid right here:

// exchange a request token for an access token
IToken accessToken = session.ExchangeRequestTokenForAccessToken(requestToken);

I already registered my application with google.