Uncaught TypeError: Cannot call method 'getRootNode' of undefined

[zvineyard]

I've downloaded and ran this nested list example but I get the following error: "Uncaught TypeError: Cannot call method 'getRootNode' of undefined." Any idea what that means?

[RelaxLloyd]

i built an identical replica version for training too, but i have the same Problem.
The json is valid and on the same webserver.

NestedListDemo.music_store = new Ext.data.TreeStore({
model: 'ListItem',
proxy: {
type: 'ajax',
url: 'Testdaten/catalouge.json', //klappt nicht?
reader: {
type: 'tree',
root: 'items'
}
}
});

[waitchen]

maybe you had wrong import sequence,
first import app.js
then item.js ,store.js, viewport.js