Message : “One or more errors occurred.” 
Source : “mscorlib”

Code Snippet :

//Create an HTTP client to send a request message to the CRM Web service.
                using (HttpClient httpClient = new HttpClient(messageHandler))
                {
                    //Specify the Web API address of the service and the period of time each request
                    // has to execute.
                    httpClient.BaseAddress = new Uri(serviceUrl);
                    httpClient.Timeout = new TimeSpan(0, 2, 0);  //2 minutes

                 
                    ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;

                    //Send the WhoAmI request to the Web API using a GET request.
                    var response = httpClient.GetAsync(“api/data/v9.0/WhoAmI”,
                            HttpCompletionOption.ResponseHeadersRead).Result;

                    if (response.IsSuccessStatusCode)
                    {
                        //Get the response content and parse it.
                        JObject body = JObject.Parse(response.Content.ReadAsStringAsync().Result);
                        Guid userId = (Guid)body[“UserId”];
                        Console.WriteLine(“Your system user ID is: {0}”, userId);
                    }
                    else
                    {
                        Console.WriteLine(“The request failed with a status of ‘{0}'”,
                               response.ReasonPhrase);
                    }
                }

Happy Coding

SOURCE : https://community.dynamics.com