[flexcoders] Flex 4, Gumbo - Could not resolve to a component implementation.

[Baz]

I am testing out Flex 4 (Gumbo) but I am receiving the error "Could not
resolve <Application> to a component implementation."

I added the SDK to my project and I also pointed the source to the
flex4.swc. Here, is my sample app that's generating the error, any ideas?

<?xml version="1.0" encoding="utf-8"?>
<Application
    xmlns:mx="library:adobe/flex/halo"
    xmlns="http://ns.adobe.com/mxml/2009";
    xmlns:gumbo="library:adobe/flex/gumbo">


    <!-- Flex 4 Hello World with FXG -->
    <mx:Canvas top="0" bottom="0" left="0" right="0">
        <Group verticalCenter="0" horizontalCenter="0">
            <TextGraphic fontFamily="Verdana" fontWeight="bold">
                <content>Hello, World</content>
            </TextGraphic>
        </Group>
    </mx:Canvas>

</Application>

Thanks,
Baz