Callback url prevents me from getting TokenSecret & Token


When i specify my callback url for the GetRequestToken() method and it’s executed, the TokenSecret & Token is null but if i don’t provide my callback url then i successfully get the TokenSecret & Token for the authorization. What’s the problem?

some live code:
TwitterService TWservice = new TwitterService(consumerKey, consumerSecret);

        String callback = Url.Action("Callback", "Twitter", null, HttpContext.Request.Url.Scheme);

        OAuthRequestToken requestToken = TWservice.GetRequestToken(callback);

thanks in advance.

PS: im using TweetSharp library


any one please give me the code for authentication of user using twitter step by step . I have tried using and

I m using abrahms php outhand i m getting internal server error 500 exact call of function getRequestToken() of twitteroauth.php.