谷歌翻译错误

我在使用Google翻译API V2时遇到了一个异常。异常文本是"远程服务器返回一个错误:(403)禁止"。调用req.GetResponse()函数时发生异常。我使用以下代码。请说明是否有正确的代码可用。由于

public static string Translate()
    {
         String textToTranslate = "Common";
         String fromLanguage = "en"; // english
         String toLanguage = "ur"; // spanish
         String apiKey = /*My API Key*/; 
        // create the url for making web request
         String apiUrl = "https://www.googleapis.com/language/translate/v2?key={0}&source={1}&target={2}&q={3}";
         String url = String.Format(apiUrl, apiKey, fromLanguage, toLanguage, textToTranslate);    
         string text = string.Empty;
        try
        {
            // create the web request
            WebRequest req = HttpWebRequest.Create(url);
            // set the request method
            req.Method = "GET";
            // get the response
            using (WebResponse res = req.GetResponse())
            {
                // read response stream
                // you must specify the encoding as UTF8 
                // because google returns the response in UTF8 format
                using (StreamReader sr = new StreamReader(res.GetResponseStream(), Encoding.UTF8))
                {
                    // read text from response stream
                    text = sr.ReadToEnd();
                }
            }
        }
        catch (Exception e)
        {
            throw; // throw the exception as is/
        }
        // return text to callee
        return text;
    }