The ILogPlugin::SetConfig method is a private interface and is used only for compatibility reasons to support RPC-based server interfaces from previous releases of IIS.
virtual HRESULT STDMETHODCALLTYPE SetConfig(
DWORD cbSize, //the size of the log configuration object
PBYTE Log //a pointer to the configuration information
);
This is a private interface method that IIS uses when it calls the built-in logging modules. Custom logging modules should return FALSE when this method is called.