We've moved the
o1 = TreeView.NodesXmlDoc.documentElement.childNodes.item(o0 - 1);
into the try-catch block some lines higher. It actually was created for catching the printing preview, but it seems that sometimes it fails (your case).
Here's a code (obfuscated though):
try
{
if (typeof(TreeView.keyEscape) == "undefined") return;
o1 = TreeView.NodesXmlDoc.documentElement.childNodes.item(o0 - 1);
}
catch(e){ return; }