[C#] Why does Range.Group() method crash after 7 calls?

[serhio]

Hello,
I have a problem with Microsoft.Office.Interop.Excel.Range.Group() method.
The problem is that I can call this method only 7 times, before it throws me an exception.
I don't understand quite well why this happens, and for witch documents this affirmation is valid, but the problem exists, probably, for a large files.
For example, if you save this file - http://serhio.atspace.com/ExcelData.xls on the drive C, and executes the following code:

        static void Main(string[] args)
        {
            Microsoft.Office.Interop.Excel.Application excelApp = new ApplicationClass();
            excelApp.Visible = true;  // Makes Excel visible to the user.
                        
            string workbookPath = @"C:\ExcelData.xls";  // Add your own path here
            // The following code opens an existing workbook
            Workbook excelWorkbook = excelApp.Workbooks.Open(workbookPath, 0,
                false, 5, "", "", false, XlPlatform.xlWindows, "", true,
                false, 0, true, false, false);
 
            // The following gets the first Woorksheet
            Worksheet worksheet = excelWorkbook.Worksheets.get_Item(1) as Worksheet;
            worksheet.Outline.SummaryRow = XlSummaryRow.xlSummaryAbove;
 
            Range aRange;
            int groupCounter = 0;
            try
            {
                for (int i = 10; i < 450; i = i + 11)
                {
                    aRange = worksheet.get_Range(string.Format("C{0}:C{1}", i, i + 10), Missing.Value);
                    aRange.Group(Missing.Value, Missing.Value, Missing.Value, Missing.Value);
                    groupCounter++;
                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

when I have groupCounter == 7, I get a
[System.Runtime.InteropServices.COMException] = {"Group method of Range class failed"}

You can skip some groups, in order to use different lines to group, but anyway, the 7-th call of Group method crashes the application.

Is there somebody qho can explain this behavior, and how can I resolve this issue?

Thanks a lot
/sergiu