New Post: NullReferenceException

tried also with GetUserFromScreenName() same problem. Tweeninvi.User is not NULL on this calls

System.NullReferenceException was caught
HResult=-2147467261
Message=Object reference not set to an instance of an object.
Source=Tweetinvi.API
StackTrace:

   at Tweetinvi.User.GetUserFromScreenName(String userName)
   at twitter.GetUserTweets() in c:\Users\www\xt\handlers\twitter2.ashx:line 57
   at twitter.ProcessRequest(HttpContext context) in c:\Users\www\xt\\handlers\twitter2.ashx:line 29

InnerException: