I just did some upgrading of an old joomla 1.0 website, installed 1.5.15, installed 1.2.1 CB, got everything OK in English, tried switching to dutch (using global language setting of Joomla, and got on every item: "Direct Access to this location is not allowed."
I found the problem, I changed the site to legacy (with Legacy plug-in) the login functioned sort-of..., checked the version of the language plug-in: 1.1.....
I now have installed the 1.2.1 language plug-in (Informal), and everything works fine!
Legacy plugin should not be needed for 1.2 CB language packs.
Install a 1.2 language pack for your language, or alternatively make sure your dutch.php and cbteamplugins_language.php also contain the defined('_JEXEC') clause at the top (compare with the default language files).