title: Duplicate "already exists" dialogs when I use SaveFileDialog and Excel.SaveAs
body: <p>I am programmatically creating an Excel file with the <code>Microsoft.Office.Interop.Excel</code> framework.  When it comes time to save, I want to give the user the choice of naming and save location, so I am using <code>System.Windows.Forms.SaveFileDialog</code>. Everything works well, except when the user chooses a filename which already exists, then both <code>SaveFileDialog.ShowDialog()</code> and <code>Excel.Application.SaveAs()</code> put up "This file already exists - are you sure you want to overwrite?" warnings, and of course 2 are not needed. I can't see a way to suppress either of them. What is the best way to fix this?</p>