Asp.net web api 有时API抛出内部服务器错误

API（第三方-它也是一个.NETWebAPI）有时抛出内部服务器错误，有时工作正常

     string api = '/api/security/create'
     var handler = new HttpClientHandler();                       
     string base_url ='https:\\abc.com\v2';
     handler.Credentials = new NetworkCredential(GetURL("authUser"), GetURL("authPW"), Domain);
                        using (var client = new HttpClient(handler))
                        {
                            if (api == null)
                            throw new Exception("Invalid URL");
    
                        client.BaseAddress = new Uri(GetURL("base_url"));
                        client.DefaultRequestHeaders.Accept.Clear();
                            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        
                            log.Info(String.Format("Submitting request to {0}/{1}", client.BaseAddress, api));
                                response = client.PutAsJsonAsync(api, objCxlle);
                                response.Wait();
                                result = response.Result;
                  if (!result.IsSuccessStatusCode)
                        {
                              //Here sometimes getting status code 500 = Internal server error
                        }
        }