https://www.dotnetzone.gr:443/cs/blogs/birbilis/archive/2015/01/26/gotcha-worksheets-property-is-read-only-sheets-is-not-excel-workbook.aspxMy contribution to: http://stackoverflow.com/questions/14109102/how-do-i-add-a-worksheet-after-all-existing-excel-worksheets   Seems Worksheets property is read-only Returns a Sheets collection that represents all the worksheets in the specifiedelCommunityServer 2.1 SP3 (Build: 20423.1)