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Exception calling 'theme_boost_union_before_session_start'

line 200 of /cache/classes/factory.php: call to core_cache\factory->create_definition()
line 190 of /cache/classes/cache.php: call to core_cache\factory->create_cache_from_definition()
line 2467 of /theme/boost_union/locallib.php: call to core_cache\cache::make()
line 862 of /theme/boost_union/lib.php: call to theme_boost_union_manipulate_hooks()
line 900 of /lib/setup.php: call to theme_boost_union_before_session_start()
line 96 of /config.php: call to require_once()
line 26 of /course/index.php: call to require_once()