New Post: 401 Unauthorized Access

I keep getting the error when trying to
run your code sample bellow. The credentials works fine when executing Curl request from
from tvitter/apps.
What could be wrong? Please help

static void Main()

    {
        var credentials = TwitterCredentials.CreateCredentials(
            ConfigurationManager.AppSettings["token_AccessToken"],
            ConfigurationManager.AppSettings["token_AccessTokenSecret"],
            ConfigurationManager.AppSettings["token_ConsumerKey"],
            ConfigurationManager.AppSettings["token_ConsumerSecret"]);

       var tweet = Tweet.CreateTweet("Xcent");
       tweet.Publish();