Core

the tcatree throws an error every time it is called. I am not into ExtJS and neither into the tcaTree itself but IMO those information should be enough to fix it.

How to test
-------------
Install EXT:news, create at least one category and call either the category record or the plugin - both got a tca tree implemented

Information from debugging
---------------------------
The error comes from class t3lib_TCEforms_Tree which got an inline JS

expandnode: function(node) {
        top.TYPO3.BackendUserSettings.ExtDirect.addToList("tcaTrees." + this.ucId, node.attributes.uid);
}

Problem is that node.attributes.uid is undefined. This happens with the root node

Using this code to debug

if (node.attributes.uid) {
    top.TYPO3.BackendUserSettings.ExtDirect.addToList("tcaTrees." + this.ucId, node.attributes.uid);
} else {
    alert(node);
}

[Node xnode-27]
[Node root]

Possible solutions ======================
As already stated, I no nothing about ExtJS but there are IMO 2 possible solutions:
1) Use an if clause "if (node.attributes.uid) {"

2) Maybe it is even more simple as IMO it should be node.attributes.id as t3lib_tree_pagetree_DataProvider also uses e.g. "$node->setId('root');" The maybe wrong value is also used in TYPO3.Components.Tree.TcaCheckChangeHandler inside tree.js