It may not be .NET, so JIC:

If you're adding sheets and/or workbooks sometimes it's necessary to do something like this (from memory):

  IF success && whatever you just created went well
    toX.Workbooks.Close() && get rid of it
  ELSE
     * error but you still gotta close up
     IF toX.Workbooks.Count > 0
        toX.Workbooks(1).Close(.F.) && do not save changes      
        toX.Workbooks.Close()   
     ENDIF
  ENDIF

  * make sure something like this occurs for each
  * sheet or book you're messing around with.

  * after this, and after nulling out all object refs,
  * then the Quit will work okay:

   toX.Quit

>L<