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The CAcTcUiToolPaletteGroup::Save(IUnknown* pUnk) is expecting a pointer to an MSXML::IXMLDOMNode. This function saves this group's definition to the XML node represented by pUnk. Only the IDs of the group's tool palettes are saved to the XML node. The tool palettes themselves must be saved separately.
I believe you can use the AcTcUi*::Export() methods to set the various output paths to disk.