New Post: How to publish tweets?

Hi, I have tried both of the post methods above, and I am getting an unauthorised message, basically, I have a stream connected to my twitter account, and based on certain key words in tweets, I respond to the tweet with a thankyou message, so I have done the following

Tweet tw = new Tweet(e.Value.Creator.ScreenName + " Thanks for selecting : " + selection);
bool tmp = tw.Publish(token);

var tokenUser = new TokenUser(token);
tokenUser.PublishTweet("@" + e.Value.Creator.ScreenName + " Thanks for selecting : " + selection); 

I have even tried to just post a simple tweet, but I am getting the following message :

{"The remote server returned an error: (401) Unauthorized."}

am I missing something really silly ?? I know the token is ok, as I receive the messages no problem.

any pointers would be much appreciated.

Thanks