Version(s) of Ext GWT
Ext GWT 3.0.1

Browser versions and OS (and desktop environment, if applicable)
IE 9 Windows 7

Virtual Machine

I can't provide a test case, but I can try to describe it. I'm filling a TreeGrid using a simple RPC call (so no proxy, loader etc - just simple getStore().add methods after onSuccess). If I change my view before the data was added, I get exactly the same exception, someone posted here already. I also debugged it, and found out, that node = null in TreeBaseAppearance.onJointChange, if I leave the view before adding data. So I overrode the TreeBaseAppearance/BlueTreeAppearance and added a null check:
        if (node != null && node.getFirstChild() != null)
            e = (Element) node.getFirstChild().insertBefore(e, jointElement);
This solved the problem. It would be great, if you could check this and modify the original source.

Run mode
Development Mode