Some of you may have noticed, that date archive widget and the BlogTree pages do not work well together. Specifically the url fragment such as '/blog/date/2011/04' doesn't work if 'blog' is a BlogTree instance, but DOES work if it is a BlogHolder instance.
Inside BlogTree.php and the BlogTree_Controler class. You need to add 'date' to the $allowed_actions array.
static $allowed_actions = array(
'index',
'rss',
'tag',
'date'
);