After Upgrade to Buddypress 1.2.6 from 1.2.5.2 , admin bar area displayed incorrectly for guest-visitors

why not contact the company who developed the theme? – they provide support for their customers.
http://premium.wpmudev.org/project/buddypress-blogsmu-theme
http://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/what-necessary-changes-should-be-made-to-bp-themes-for-bp-1-2-6/

Maybe the theme was not tested/compatible with bp1.2.6 yet or have issued an update since.