Encountered a communication error (https://api.myob.com/accountright)

Hi, 
I am trying to fetch the accounts using my .NET application, built over the same version as MYOB SDK.
When I hit the API I get "a communication error (https://api.myob.com/accountright)" like this

How can I resolve this error and what should I do for that?
 
Code: 

public ActionResult GetContacts()
        {
            try
            {
                var accessToken = HttpContext.Request.Headers["Authorization"].ToString().Replace("Bearer ", "");
                var expiresIn = HttpContext.Request.Headers["ExpiresIn"];
                var hasExpired = HttpContext.Request.Headers["HasExpired"];
                var receivedTime = HttpContext.Request.Headers["ReceivedTime"];
                var refreshToken = HttpContext.Request.Headers["RefreshToken"];
                var scope = HttpContext.Request.Headers["Scope"];
                var tokenType = HttpContext.Request.Headers["TokenType"];

                var tokenValues = new TokenValues
                {
                    AccessToken = accessToken,
                    ExpiresIn = int.Parse(expiresIn),
                    HasExpired = bool.Parse(hasExpired),
                    ReceivedTime = DateTime.Parse(receivedTime),
                    RefreshToken = refreshToken,
                    Scope = scope,
                    TokenType = tokenType
                };

                var tokenValuesJson = JsonConvert.SerializeObject(tokenValues);
                var keystore = JsonConvert.DeserializeObject<SimpleOAuthKeyService>(tokenValuesJson);

                // Fetch a list of company files
                var cfService = new CompanyFileService(_configuration, null, keystore);
                var companyFiles = cfService.GetRange();
                // Select a company file
                var companyFile = companyFiles.FirstOrDefault(x => new Version(x.ProductVersion) >= new Version("2013.3"));
                if (companyFile == null)
                {
                    return HttpNotFound("No company file found that supports version 2 of the AccountRight API.");
                }

                // Fetch accounts for the selected company file
                var credentials = new CompanyFileCredentials("Administrator", "");
                var accountService = new MYOB.AccountRight.SDK.Services.GeneralLedger.AccountService(_configuration, null, keystore);
                var accounts = accountService.GetRange(companyFile, null, credentials);
                return Ok(accounts);

            }
            catch (Exception ex)
            {
                Console.WriteLine("Error in GetContacts: " + ex.Message);
                Console.WriteLine("Stack trace: " + ex.StackTrace);
                return new HttpStatusCodeResult(500, "Internal Server Error: " + ex.Message);
            }
        }