Is your KML file publicly accessible? This is the second thread where I have read that the KML file needs to be publicly available. I find it very frustrating that this is not explicitly mentioned in the documentation. For example, http://help.arcgis.com/en/webapi/javascript/arcgis/help/jssamples_start.htm#jssamples/layers_kmlbuffer.html and http://help.arcgis.com/en/webapi/javascript/arcgis/help/jssamples/layers_kml.html Should probably be modified to mention this very important piece of information!
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