OAuth2Parameters could not be found

I'm trying to use OAuth 2.0 for authorizing google docs API, According to the example given by google at https://developers.google.com/google-apps/documents-list/#authorizing_requests_with_oauth_20 they are using the piece of code: ``` // OAuth2Parameters holds all the parameters related to OAuth 2.0. OAuth2Parameters parameters = new OAuth2Parameters(); // Set your OAuth 2.0 Client Id (which you can register at // https://code.google.com/apis/console). parameters.ClientId = CLIENT_ID; // Set your OAuth 2.0 Client Secret, which can be obtained at // https://code.google.com/apis/console. parameters.ClientSecret = CLIENT_SECRET; // Set your Redirect URI, which can be registered at // https://code.google.com/apis/console. parameters.RedirectUri = REDIRECT_URI; //////////////////////////////////////////////////////////////////////////// // STEP 3: Get the Authorization URL //////////////////////////////////////////////////////////////////////////// // Set the scope for this particular service. parameters.Scope = SCOPE; // Get the authorization url. The user of your application must visit // this url in order to authorize with Google. If you are building a // browser-based application, you can redirect the user to the authorization // url. string authorizationUrl = OAuthUtil.CreateOAuth2AuthorizationUrl(parameters); ``` Problem is that when I try to use this code it says that OAuth2Parameters couldn't be found I'm using both `Google.GData.Client`; & `Google.GData.Documents`; What to do here??