Paypal Invoice SDK Service Call + Express Checkout + Recurrying Payment issue

Question

Hi I have implemented Paypal Invoice, Express Checkout & Recurring Payments services using adaptive methods (NVP) call. It is working fine on my local system with sandbox account but not on development server and facing problem wherever I have called the paypal services based on request.

Code

    InvoiceModelAlias.PaymentTermsType paymentTermsType = (InvoiceModelAlias.PaymentTermsType)Enum.Parse(typeof(InvoiceModelAlias.PaymentTermsType),invoice.PaymentTerms.ToUpper());
    InvoiceModelAlias.CreateAndSendInvoiceRequest invoiceRequest = new InvoiceModelAlias.CreateAndSendInvoiceRequest();  
    invoiceRequest.requestEnvelope = new InvoiceModelAlias.RequestEnvelope();
    invoiceRequest.requestEnvelope.errorLanguage = "en_US";
    invoiceRequest.invoice = new InvoiceModelAlias.InvoiceType();
    invoiceRequest.invoice.currencyCode = invoice.CurrencyCode;
    invoiceRequest.invoice.merchantEmail = invoice.MerchantEmail;
    invoiceRequest.invoice.payerEmail = invoice.PayerEmail;
    invoiceRequest.invoice.paymentTerms = paymentTermsType;
    invoiceRequest.invoice.itemList = new InvoiceModelAlias.InvoiceItemListType();
    invoiceRequest.invoice.itemList.item = new List<InvoiceModelAlias.InvoiceItemType>();
    invoiceRequest.invoice.itemList.item.Add(new InvoiceModelAlias.InvoiceItemType(invoice.ItemName, Convert.ToDecimal(invoice.ItemQuantity), Convert.ToDecimal(invoice.ItemAmount)));
    InvoiceAlias.InvoiceService invoiceService;
    InvoiceModelAlias.CreateAndSendInvoiceResponse invoiceResponse = null;
    invoiceService = GetService();
    invoiceResponse = invoiceService.CreateAndSendInvoice(invoiceRequest);
    string ackRsponse = invoiceResponse.responseEnvelope.ack.ToString();

invoiceService.CreateAndSendInvoice(invoiceRequest)

Exception

PayPal.Exception.ConnectionException: Invalid HTTP response The underlying connection was closed: An unexpected error occurred on a receive.
   at PayPal.HttpConnection.Execute(String payLoad, HttpWebRequest httpRequest)
   at PayPal.APIService.MakeRequestUsing(IAPICallPreHandler apiCallHandler)
   at PayPal.BasePayPalService.Call(IAPICallPreHandler apiCallHandler)
   at PayPal.Invoice.InvoiceService.CreateAndSendInvoice(CreateAndSendInvoiceRequest createAndSendInvoiceRequest, String apiUserName)
   at PayPal.Invoice.InvoiceService.CreateAndSendInvoice(CreateAndSendInvoiceRequest createAndSendInvoiceRequest)
   at DoPayments.Payments.Invoices.CreateAndSendInvoice(Invoice invoice)

Will you please someone help me to get this out or suggest whats the reason behind this as it is working fine at local but not on development/production server.

Same kind of issue I am facing in case of express checkout and recurring payment methods too which is below:

com.paypal.sdk.exceptions.FatalException: The underlying connection was closed: An unexpected error occurred on a receive.
   at com.paypal.sdk.core.nvp.NVPAPICaller.Call(String NvpRequest)
   at com.paypal.sdk.services.NVPCallerServices.Call(String requestnvp)

Thanks in advance.