InvalidCastException - Unable to cast COM object of type 'Microsoft.Office.Interop.Outlook.ApplicationClass'

Question

I have written this code to send attached file using outlook from my .net application and here is the code:

Microsoft.Office.Interop.Outlook.Application outlook = new Microsoft.Office.Interop.Outlook.Application();
            Microsoft.Office.Interop.Outlook.Application session = new Microsoft.Office.Interop.Outlook.Application();
            Microsoft.Office.Interop.Outlook.NameSpace ns = outlook.Session;
            Outlook.MailItem mail = outlook.Application.CreateItem(Outlook.OlItemType.olMailItem) as Outlook.MailItem;
            mail.Subject = txtSubject.Text;
            mail.To = txtTo.Text;
            mail.Subject = txtSubject.Text;
            mail.Body = txtBody.Text;
            mail.Attachments.Add(@"c:\Users\admin\Desktop\Excel.txt",
                    Outlook.OlAttachmentType.olByValue, Type.Missing,
                    Type.Missing);
            Outlook.Accounts accounts = outlook.Session.Accounts;

            foreach (Outlook.Account account in accounts)
            {
                // When the e-mail address matches, send the mail.
                if (string.Equals(account.SmtpAddress, txtFrom.Text, StringComparison.OrdinalIgnoreCase))
                {
                    mail.SendUsingAccount = account;
                    mail.Save();
                    ((Outlook._MailItem)outlook).Send();
                    lblStatus.Text = "Report Sent";
                    break;
                }
            }

But when it reaches to the Send()method call, I get this error:

Unable to cast COM object of type 'Microsoft.Office.Interop.Outlook.ApplicationClass' to interface type 'Microsoft.Office.Interop.Outlook._MailItem'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{00063034-0000-0000-C000-000000000046}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).

Answer 1

You are casting the wrong object

outlook is defined as Microsoft.Office.Interop.Outlook.Application

You need to change

((Outlook._MailItem)outlook).Send();

to:

((Outlook._MailItem)mail).Send();

Reference