I receive the following error:

    System.NullReferenceException

      HResult=0x80004003
      Message=Object reference not set to an instance of an object.
      Source=BaptistTrumpetInvoicingV2
      StackTrace:
       at EOL.BaptistTumpetInvoicing.GenerateSubscriptionInvoices.AddQBInvoice(Customer objCustomer) in E:\web\dnndev.me\Website\DesktopModules\BaptistTrumpetInvoicingV2\GenerateInvoices.cs:line 724
    (line 724 is:  objInvoice.InvoiceLineItems.Add(objLineItem);)

When running the AddQBInvoice method:

        public string AddQBInvoice (Customer objCustomer)

        {
            string strReturn = "";
            Invoice objInvoice = new Invoice();

            objInvoice.CustomerRefId = objCustomer.Id;

            objInvoice.CustomerRefName = objCustomer.DisplayName;
            objInvoice.Id = "300";

            bTQBContext.Invoices.Add(objInvoice);

            /* Try adding Invoice w/o adding the InvoiceLineItem*/

            InvoiceLineItem objLineItem = new InvoiceLineItem();
            objLineItem.Id = "300-1";
            objLineItem.Amount = 0;
            objLineItem.LineNum = 1.0m;
            objLineItem.Description = "Donations";
            objLineItem.DetailType = "SalesItemLineDetail";
            objLineItem.SalesItemLineDetailItemRefId = "21";
            objLineItem.SalesItemLineDetailItemRefName = "Donations";
            objLineItem.SalesItemLineDetailUnitPrice = 0.0m;
            objLineItem.SalesItemLineDetailQty = 0.0m;
            objLineItem.SalesItemLineDetailTaxCodeRefId = "TAX";             objInvoice.InvoiceLineItems.Add(objLineItem);

            //bTQBContext.Invoices.

            strReturn = objInvoice.Id;

            return strReturn;
        }