Along similar lines as, I'm also getting this error on a fresh Aurora theme install:
Notice: Undefined index: sidebar_first in include() (line 131 of /var/aegir/platforms/panopoly-beta5/sites/all/themes/aurora/templates/system/page.tpl.php).
I've commented out the line in the page.tpl.php file for now. However this is odd that, while the region is declared in the mytheme.info file, it is not showing up on my blocks page (see attached), wonder why this would happen?
# Regions regions[sidebar_first] = Primary Sidebar regions[sidebar_second] = Secondary Sidebar regions[content] = Content