如何解决403错误在谷歌分析API调用

我在下面的帖子中使用代码:Google Analytics API -在服务器端以编程方式获取页面浏览量

但是在下面高亮显示的行上得到一个403 forbidden错误。我不认为这是一个凭证问题，因为我的凭证是正确的，因为我已经检查和再次检查了，并且我用这些凭证登录了分析帐户。所以可能是文件夹权限问题?

//-------------- Get Auth Token -------------------
WebClient webClient = new WebClient();
NameValueCollection data = new NameValueCollection();
data.Add("accountType", "GOOGLE");
data.Add("Email", "xxxx@gmail.com");
data.Add("Passwd", "xxxx");//Passwd, not a misspell.
data.Add("service", "analytics");
data.Add("source", "xxxx-xxxx-xx");//Could be anything.
byte[] bytes = webClient.UploadValues("https://www.google.com/accounts/ClientLogin", "POST", data);
string tokens = Encoding.UTF8.GetString(bytes);
string authToken = extractAuthToken(tokens);
//-------------- Get page views -------------------
string feed = "https://www.google.com/analytics/feeds/data";
//Required:
string ids = "ga:xxxx";
string metrics = "ga:pageviews";
string startDate = "2011-06-25";
string endDate = "2011-07-25";
//Optional:
string dimensions = "ga:pagePath";
string sort = "-ga:pageviews";            
string feedUrl = string.Format("{0}?ids={1}&dimensions={2}&metrics={3}&sort={4}&start-date={5}&end-date={6}",
    feed, ids, dimensions, metrics, sort, startDate, endDate);
webClient.Headers.Add("Authorization", "GoogleLogin " + authToken);
// This is the line I get the 403 error on:
**string result = webClient.DownloadString(feedUrl);**
//-------------- Extract data from xml -------------------
XDocument xml = XDocument.Parse(result);
var ns1 = "{http://www.w3.org/2005/Atom}";
var ns2 = "{http://schemas.google.com/analytics/2009}";
var q = from entry in xml.Descendants()
        where entry.Name == ns1 + "entry"
        select new
        {
            PagePath = entry.Element(ns2 + "dimension").Attribute("value").Value,
            Views = entry.Element(ns2 + "metric").Attribute("value").Value
        };
//-------------- Do something with data -------------------
foreach (var page in q)
{
    Debug.WriteLine(page.PagePath + " " + page.Views);                
}
//-------------- Help Method -------------------
private string extractAuthToken(string data)
{          
    var tokens = data.Split(new string[] { "'n" }, StringSplitOptions.RemoveEmptyEntries);            
    return tokens.Where(token => token.StartsWith("Auth=")).Single();
}