C#

using Core = Microsoft.Office.Core;
using Word = Microsoft.Office.Interop.Word;
using Excel = Microsoft.Office.Interop.Excel;

        private void button1_Click(object sender, EventArgs e)
        {
            object oMissing = System.Reflection.Missing.Value;
            Word.Application app = new Word.ApplicationClass();
            app.Visible = true;
            Word.Document doc = app.Documents.Add(ref oMissing, ref oMissing, ref oMissing, ref oMissing);
            Word.Range rng = doc.Content;
            rng.InsertAfter("Some text.");
            rng.InsertParagraphAfter();
            rng.InsertAfter("new paragraph");
        }

        private void button2_Click(object sender, EventArgs e)
        {
            try
            {
                object oMissing = System.Reflection.Missing.Value;
                Excel.Application app = new Excel.ApplicationClass();
                app.Visible = true;
                Excel.Workbook wb = app.Workbooks.Add(oMissing);//here is the error
            }
            catch (Exception error)
            {
                MessageBox.Show(error.ToString());
            }
        }