Installed commons 3.8 on Xubuntu 3.10 with PHP 5.5.3: got lots of these Notices:

Notice: Array to string conversion in panels_cache_object->cache()
(line 183 of /.../profiles/commons/modules/contrib/panels/includes/plugins.inc).

Applied patch at https://drupal.org/comment/8262211#comment-8262211 and problem went away.