New Post: Get previous tweets

hI linvi, i'm trying to get the lastest 4 tweets for a specific tweet posted in a specific screen, in my case mteodoro85.

what query should i use.

var searchQuery = Search.GenerateSearchTweetParameter("@mteodoro85");
searchQuery.MaximumNumberOfResults = 4;
var results = Search.SearchTweets(searchQuery);

this code returns the error
Value cannot be null.
Parameter name: s

Regars,
Marco