Delphi outlook获取错误消息为“无效的类字符串”

Question

program MailWithOutlook;    
procedure SendOutlookMail;
const
  olMailItem = 0;
var
  Outlook: OleVariant;
  vMailItem: variant;
begin
  try
    Outlook := GetActiveOleObject('Outlook.Application'); // error occurs on here as "Invalid Class string"
  except
    Outlook := CreateOleObject('Outlook.Application');
  end;
  vMailItem := Outlook.CreateItem(olMailItem);
  vMailItem.Recipients.Add('nitinshevale555@gmail.com');
  vMailItem.Subject := 'test email';
  vMailItem.Body := 'This is a test';
  vMailItem.Attachments.Add('C:\temp\sample.txt');
  vMailItem.Send;    
  VarClear(Outlook);
end;
end.

请建议使用Delphi 7通过Outlook发送电子邮件的任何解决方案。 展望也是开放的。我认为这是注册表文件的版本错误。但没有得到实际的结果。