I don't think I've explained the problem well enough. I am doing all of this
in a C# web forms program by automating Excel using the Interop libraries.
The spreadsheet to be saved is being created and saved by that program
without user intervention. Here is the call that works in XP but not in
Vista:

theName = "FinalReport" +
String.Format("{0:yyyyMMddhhmmssttt}", DateTime.Now) + ".xls";


oSheet.SaveAs(Environment.GetFolderPath(Environmen t.SpecialFolder.InternetCache) + @"\" + theName,
Excel.XlFileFormat.xlExcel7, Type.Missing, Type.Missing,
Type.Missing, Type.Missing,
Type.Missing, Type.Missing, Type.Missing);