Try this:
...
<mx:Component>
<mx:VBox>
<mx:Script>
<![CDATA[
import valueObjects.ShoppingCartItem
]]>
</mx:Script>
<mx:Button
label="Remove"
click="outerDocument.removeItem(valueObjects.ShoppingCartItem(data));" />
</mx:VBox>
</mx:Component>
...This gives the outerDocument method the visibility to the ShoppingCartItem component from within the VBox.

