Request for principal permission failed

Hi,

Using Microsoft Identity and implemented Vote application from this article. 

But I getting error in my http handler when trying to create repository. 

Any idea?

<%@ WebHandler Language="C#" Class="Vote" %>

using System;
using System.Web;
using System.Web.Security;
using System.Security.Permissions;
using System.Web.Script.Serialization;
using Microsoft.AspNet.Identity;

[PrincipalPermission(SecurityAction.Demand, Authenticated = true)]
public class Vote : IHttpHandler {

    public void ProcessRequest (HttpContext context) {
        // Make sure voteValue is -1, 0, or 1
        if (string.IsNullOrEmpty(context.Request.QueryString["articleId"]))
            throw new ArgumentException("articleId not supplied");
        if (string.IsNullOrEmpty(context.Request.QueryString["voteValue"]))
            throw new ArgumentException("voteValue not supplied");

        var articleId = Convert.ToInt32(context.Request.QueryString["articleId"]);
        var voteValue = Convert.ToInt32(context.Request.QueryString["voteValue"]);

        if (voteValue < -1 || voteValue > 1)
            throw new ArgumentException(string.Format("Invalid voteValue, {0}. Expected -1, 0, or 1.", voteValue));

        if (HttpContext.Current.User.Identity.IsAuthenticated)
        {
            var userId = HttpContext.Current.User.Identity.GetUserId();
                
            // Record the vote and get the new cumulative vote score for this article
            var newVoteScore = ArticleRepository.Vote(articleId, voteValue, userId);

            // Return the new cumulative vote score for this article        
            var jsonSerializer = new JavaScriptSerializer();
            context.Response.ContentType = "application/json";
            context.Response.Write(jsonSerializer.Serialize(new { NewVoteScore = newVoteScore }));
        }
    }

    private ArticleRepository _articleRepository = null; //Error in here "Request for principal permission failed"
    public ArticleRepository ArticleRepository
    {
        get
        {
            if (_articleRepository == null)
                _articleRepository = new ArticleRepository();

            return _articleRepository;
        }
    }

    public bool IsReusable {
        get {
            return false;
        }
    }

}