As found when logging in as admin to http://qa.moodle.net/

[MAIN CONTENT GOES HERE - fvdEjPjWcD]

Coding error detected, it must be fixed by a programmer: Trying to reference an unknown block region side-pre

Debug info:
Error code: codingerror
Stack trace:

line 884 of /lib/blocklib.php: coding_exception thrown
line 984 of /lib/blocklib.php: call to block_manager->check_region_is_known()
line 997 of /lib/blocklib.php: call to block_manager->ensure_instances_exist()
line 315 of /lib/blocklib.php: call to block_manager->ensure_content_created()
line 1232 of /lib/outputrenderers.php: call to block_manager->get_content_for_region()
line 3053 of /lib/outputrenderers.php: call to core_renderer->blocks_for_region()
line 96 of /theme/clean/layout/columns3.php: call to core_renderer->blocks()
line 847 of /lib/outputrenderers.php: call to include()
line 777 of /lib/outputrenderers.php: call to core_renderer->render_page_layout()
line 101 of /index.php: call to core_renderer->header()

Unfortunately the problem doesn't seem to have been solved by MDL-40065.