TweetSharp not allowing a search - Could not load file or assembly

Question

I am having problems running the following code. Authentication works fine but it fails on the search every time. Any help would be appreciated:

Console.WriteLine("Bot started: " + DateTime.Now);
            service  = new TwitterService(customerKey, customerKeySecret);
            service.AuthenticateWith(accessToken, accessTokenSecret);

            TwitterSearchResult tweets = service.Search(new SearchOptions { Q = "#FF", Count = 100 });

            if (tweets != null)
            {

                foreach (var tweet in tweets.Statuses)
                {
                    Console.WriteLine("{0} says '{1}", tweet.User.ScreenName, tweet.Text);
                }
            }
            else
            {
                Console.WriteLine("FAIL");
            }

            Console.Read();
            Console.WriteLine("Done");

The error looks like this:

Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly 'System.Security.Permissions, Version=0.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'. The system cannot find the file specified.

I've tried adding the using directive System.Security.Permissions, although it isn't used. Still no luck.