WPMU: You do not have sufficient permissions to access this page.

While moving, a blog from WPMU to a single wordpress, I kept getting this message: "You do not have sufficient permissions to access this page." I have played for about an hour with wp_usermeta and wp_users. Tested all kinds of settings in wp_capabilities and wp_user_level but still nothing worked. Then I have spotted it in wp_options. The option_name wp_user_roles was missing and instead was something like wp_123_user_roles. After I renamed it, all worked like a charm.