Sequence contains more than one element

<ul id="myTab" class="nav nav-tabs">
    @{ var group = Model.GroupBy(g => g.ReviewID).ToList(); }
    @foreach (var item in group)                
    {
      string active = @group.First() == item ? "active" : string.Empty;

      <li class="@active"><a href="#@Model.Where(a => a.ReviewID ==      item.Key).Single().Review.PersonID" data-toggle="tab"></a></li>
     }
     <li class="form-group pull-right">
        <div class="col-md-offset-1 col-md-12">
     <input type="submit" value="Submit" class="btn btn-primary btn-default" name="Add" />
    </div>
  </li>
</ul>

public ActionResult Index()
        {
            DateTime dateToday = DateTime.Now;
            DateTime firstOfThisMonth = new DateTime(dateToday.Year, dateToday.Month, 1);

            string name = User.Identity.Name;
            string newName = GetUserName(name);

            var unansweredReviews = from ur in db.Reviews
                                    where ur.PersonID == newName
                                    where ur.Responses.Any(s => s.ScoreID == null)
                                    select ur;

            if(unansweredReviews.Any())
            {
                return View(unansweredReviews.SelectMany(u => u.Responses).ToList());
            }

            var reviewForCurrentMonth = from cm in db.Reviews
                            where cm.PersonID == newName
                            where cm.DateTimeReviewed != null && cm.DateTimeReviewed <= firstOfThisMonth
                            select cm;

            if(reviewForCurrentMonth.Any())
            {
                Response.Redirect("~/Home/Index");
            }
            else
            {
                var getQuestions = db.Questions.Select(q => q.QuestionID);
                var peersToReview = db.People.Where(p => p.PersonID == newName).Single().MemberGroups.SelectMany(rg => rg.Members).ToList();

                foreach (var peers in peersToReview)
                {
                    Review reviews = new Review();
                    reviews.PersonID = newName;
                    reviews.ReviewPersonID = peers.PersonID;
                    foreach (var id in getQuestions)
                    {
                        Response responses = new Response();
                        responses.Review = reviews;
                        responses.QuestionID = id;
                        db.Responses.Add(responses);
                    }
                    db.Reviews.Add(reviews);
                } 
                db.SaveChanges();
            }
            return View();
        }