In a VB.Net program I am opening an Excel workbook, adding some data,
and then saving the file. My code is:

Dim xlApp As New Excel.Application
Dim wb As Excel.Workbook
Dim ws As Excel.Worksheet

' Code to add data here.

wb.Save()
xlApp.Quit()
xlApp = Nothing
       
The problem is that sometimes, but not all the time, the call to Save()
pops up a dialog box telling me that the file already exists and asking
if I want to replace it. THis is not supposed to happen with Save().
What could be causing this?