Update twitter status using oauth

Question

I am trying to update status from my c# application using oauth.

At first i am able to update the status successfully where the oauth has oauth_token, and oauth_token_secret

//Get the access token and secret.
            oAuth.AccessTokenGet(Request["oauth_token"]);

            if (oAuth.TokenSecret.Length > 0)
            {
                //We now have the credentials, so make a call to the Twitter API.
                url = "http://twitter.com/account/verify_credentials.xml";
                xml = oAuth.oAuthWebRequest(oAuthTwitter.Method.GET, url, String.Empty);
                //apiResponse.InnerHtml = Server.HtmlEncode(xml);

                //POST Test
                url = "http://twitter.com/statuses/update.xml";
                xml = oAuth.oAuthWebRequest(oAuthTwitter.Method.POST, url, "status=" + oAuth.UrlEncode( TextBox1.Text));
                //apiResponse.InnerHtml = Server.HtmlEncode(xml);
                //apiStatus.InnerHtml = Server.HtmlEncode(xml);
            }

when i try to update the status again with the same oauth, the application is requesting oAuth.AccessTokenGet method. how can i use the same oauthtoken and oauthtoken_secret that i have at the first time and post the message.

I can store the values in a session, but can some one post me the code for the status update.