see user post with error:
we have to investigate. it seems Piwik_LanguagesManager->getLanguageToLoad tries to get the user login before the access object was created, in frontcontroller line 237: Piwik_Translate::getInstance()->loadUserTranslation();
access is created line 258.
I don't know why it's not failing for other users.
(In ) - fix #605 error after installation: user translation tries to use 'access' before it's loaded