// when I click on this
    $(".like_post").on("click", function () {
        var PostId = $(this).attr("data-item");
        console.log("You Liked post #" + PostId);
        $.post("/Post/Like", PostId, function (data) {
            if (data.Data.IsOk) {
                $(this).closest(".likes").html($(this).closest("likes").html() + 1);
            }
            else
            {
                showMessage(data.Data.Title, data.Data.Message);
            }
        });
    });

// I get an internal server error and the Controller Action (below) doesn't get hit

[HttpPost]
public JsonResult Like(int postId)
{
    try
    {
        // create a new Like
        Opinion Like = new Opinion()
        {
            Direction = true,
            PostId = postId,
            UserId = UserId
        };


        var PostOpinions = db.Opinions.Where(x => x.PostId == postId && x.UserId == UserId);
        if (PostOpinions != null)
        {
            // add the Like only if the user hasn't already Liked the post
            db.Opinions.Add(Like);
            db.SaveChanges();

            return CreateResponseMessage(Json(new { IsOk = true, PostId = postId, Liked = true }), true);
        }
        else
        {
            // if the user has already Liked the post, remove the Like
            db.Opinions.Remove(Like);
            return CreateResponseMessage(Json(new { IsOk = true, PostId = postId, Liked = false }), true);
        }
    }
    // catch goes here
}