Llew,did you modify the dojoConfig flags in the main html file (viewer.html)?please check that isDebug is set to false in dojoConfig in viewer.html.<script>
var dojoConfig = {
locale: 'en',
isDebug: false,
packages: [
{ name: "esri", location: "../../esri" },
{ name: "WebScene", location: "../../WebScene" }
]
};
</script>