to fix:

Code:
    selectPath : function(path, attr, callback){
        attr = attr || "id";
        var keys = path.split(this.pathSeparator);
        var v = keys.pop();
        if(keys.length > 0){
            var f = function(success, node){
needs to be:

Code:
    selectPath : function(path, attr, callback){
        attr = attr || "id";
        var keys = path.split(this.pathSeparator);
        var v = keys.pop();
        if(keys.length > 1){
            var f = function(success, node){
test case:
Code:
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
        <title>Reorder TreePanel</title>
            <link rel="stylesheet" type="text/css" href="http://extjs.com/deploy/dev/resources/css/ext-all.css" />    
             <link rel="stylesheet" type="text/css" href="http://extjs.com/deploy/dev/resources/css/xtheme-default.css" /><!-- LIBS -->
             <script type="text/javascript" src="http://extjs.com/deploy/dev/adapter/ext/ext-base.js"></script>
            <script type="text/javascript" src="http://extjs.com/deploy/dev/ext-all.js"></script>
            <link rel="stylesheet" type="text/css" href="http://extjs.com/deploy/dev/examples/shared/examples.css" />
            <script language="javascript" type="text/javascript">
                Ext.onReady(function(){
                    // shorthand
                    var Tree = Ext.tree;
                    
                    var tree = new Tree.TreePanel({
                        el:'tree-div',
                        useArrows:true,
                        autoScroll:true,
                        animate:true,
                        enableDD:true,
                        containerScroll: true,
                
                        root: {
                            text: 'Ext JS',
                            draggable:false,
                            id:'source'
                        }
                    });
                
                    // render the tree
                    tree.render();
                    tree.selectPath(tree.getRootNode().getPath('id'), 'id', function(success, node) {
                        alert('success = ' + success)
                    });
                });
        </script>
    </head>
    <body>
        <div id="tree-div" style="overflow:auto; height:300px;width:250px;border:1px solid #c3daf9;"></div>
    </body>
</html>