Thread:Extension talk:CategoryTree/Javascript error loading the tree in the sidebar

I have the extension working, and have now the config:
 * $wgUseAjax = true;
 * require_once( "$IP/extensions/CategoryTree/CategoryTree.php" );
 * $wgCategoryTreeDynamicTag = true;
 * $wgCategoryTreeSidebarRoot = '[my top level category]';
 * $wgCategoryTreeForceHeaders = true;

When loaded the in-page tree loads fine, the categories heading appears for the portlet, but nothing else. The javascript console reports that categoryTreeloadChildren is undefined.

Using 1.21 on Chrome

any help appreciated