It's not so much what Visual LISP wants, as opposed to it trying to honour what excel wants. Ackkk, sorry to go semantic on you.
Anyway, if you open Excel and drill into the object model you'll find the SaveAs method defined thusly --
SaveAs([Filename], [FileFormat], [Password], [WriteResPassword], [ReadOnlyRecommended], [CreateBackup], [AccessMode As XlSaveAsAccessMode = xlNoChange], [ConflictResolution], [AddToMru], [TextCodepage], [TextVisualLayout], [Local])
Nice concise parameter list. Wait, there's more:
Filename - Optional Variant. A string that indicates the name of the file to be saved. You can include a full path; if you don't, Microsoft Excel saves the file in the current folder.
FileFormat - Optional Variant. The file format to use when you save the file. For a list of valid choices, see the FileFormat property. For an existing file, the default format is the last file format specified; for a new file, the default is the format of the version of Excel being used.
Password - Optional Variant. A case-sensitive string (no more than 15 characters) that indicates the protection password to be given to the file.
WriteResPassword - Optional Variant. A string that indicates the write-reservation password for this file. If a file is saved with the password and the password isn't supplied when the file is opened, the file is opened as read-only.
ReadOnlyRecommended - Optional Variant. True to display a message when the file is opened, recommending that the file be opened as read-only.
CreateBackup - Optional Variant. True to create a backup file.
AddToMru - Optional Variant. True to add this workbook to the list of recently used files. The default value is False.
TextCodePage - Optional Variant. Not used in U.S. English Microsoft Excel.
TextVisualLayout - Optional Variant. Not used in U.S. English Microsoft Excel.
Local - Optional Variant. True saves files against the language of Microsoft Excel (including control panel settings). False (default) saves files against the language of Visual Basic for Applications (VBA) (which is typically US English unless the VBA project where Workbooks.Open is run from is an old internationalized XL5/95 VBA project).