>Actual code might be useful......

Sure. Enjoy, if that's the word :)

This was the problem:
>>I prepare a table in Excel within a Using () statement. At the end I UsedRange.Copy() to what I understand is the clipboard. Then I Selection.PasteExcelTable in a Word document.
>>I get an COM Exception "command failed".
>>When I activate the word document and press Ctrl+V the table gets copied.
>>I wonder if that has something to do with the fact that maybe I must reactivate the Word document in code.
>>The word document gets created also within a Using() statement. I execute the Excel procedure from within the Using(Word) statement.
>>
>>I tried the Activate method of the Word.Application object and also when I wait for 5 seconds after the Activate().


The method that opens Word. Test_ComputeTotalDifference() is a method that calls Excel (see below). AddClopboard (see below) is the statement that breaks.

        public static void Test_Word()
        {
            Test_ComputeTotalDifference();
            using (var w = new WordWrapper())
            {
                w.App.Visible = true;
                w.Doc = w.Docs.Add();
                w.Sel = w.App.Selection;
                w.SetNarrowMargins();
                w.Title("Inventory Monitor (PIMON)");
                w.Heading2("1. Overall Discrepancies");
                
                w.AddClipboard();
                w.Heading2("2. Carat Discrepancies");
                w.Doc.SaveAs(@"C:\docs\WordTest.docx");
            }
        }

The code breaks here (a method of WordWrapper, see below

       public void AddClipboard()
        {
            App.Activate();
            System.Threading.Thread.Sleep(5000);
            Sel.PasteExcelTable(false,false, false);
            var t = Sel.Tables[Sel.Tables.Count];
            t.Range.Select();           
            Sel.set_Style(App.ActiveDocument.Styles["No Spacing"]);
            t.AutoFitBehavior(Word.WdAutoFitBehavior.wdAutoFitContent);
            Doc.Paragraphs.Add().Range.Select();
            Sel.set_Style(App.ActiveDocument.Styles["No Spacing"]);
            Sel.TypeText("\n");
        }

Here's the method that creates the excel sheet and copies it to the clipboard

        public static void Test_ComputeTotalDifference()
        {
            Serialization.Deserialize();
            using (var xl = new ExcelWrapper())
            {
                xl.wb = xl.wbs.Add();
                xl.ws = xl.wb.ActiveSheet;

... snip ...
                xl.ws.UsedRange.CopyPicture();

            }
        }

Here's the excelwrapper class that gets initialized with a Using

    public class ExcelWrapper : IDisposable
    {
        public enum Formats {decimal2,decimal0,date,text}
        public Excel.Application app;
        public Excel.Workbooks wbs;
        public Excel.Workbook wb;
        public Excel.Worksheets wss;
        public Excel.Worksheet ws;
        public Excel.Range rng;
        public bool mustQuit = true;
        CultureInfo originalCulture;
        Thread thread;
        
        bool disposed = false;
        #region "Dispose"
        public ExcelWrapper()
        {
            thread = Thread.CurrentThread;
            originalCulture = thread.CurrentCulture;
            app = new Excel.Application();
            app.DisplayAlerts = false;
            wbs = app.Workbooks;
        }
        void releaseObject(object o)
        {
            if (o == null) 
            {
                return;
            }
            System.Runtime.InteropServices.Marshal.FinalReleaseComObject(o);
        }
        public void Dispose() {
            if (disposed){
                return;
            }
            // try { wb.Close(); } finally { }
            if (mustQuit) {
                app.Quit();
            }
            releaseObject(rng);
            releaseObject(ws);
            releaseObject(wss);
            releaseObject(wb);
            releaseObject(wbs);
            thread.CurrentCulture = originalCulture;
            disposed = true;
        }
       ~ExcelWrapper()
        {   
        	Dispose();
        }

Similarly here is the Wordwrapper.

        public WordWrapper()
        {
            thread = Thread.CurrentThread;
            App = new Word.Application();
            App.DisplayAlerts = Microsoft.Office.Interop.Word.WdAlertLevel.wdAlertsNone;
            Docs = App.Documents;
        }
        void releaseObject(object o)
        {
            if (o == null)
            {
                return;
            }
            System.Runtime.InteropServices.Marshal.FinalReleaseComObject(o);
        }
        public void Dispose()
        {
            if (disposed)
            {
                return;
            }
            // try { wb.Close(); } finally { }
            if (MustQuit)
            {
                App.Quit();
            }
            releaseObject(Doc);
            releaseObject(Docs);
            disposed = true;
        }
        ~WordWrapper()
        {
            Dispose();
        }