In the WordPress install i work on we don't use the standard directory structure. WordPress allows you to move the wp-content, plugins and themes directory as long as you tell wordpress in the wp_config file where you've moved them too.
On line 168 of /modules/module.post-type.php file and line 599 of /modules/module.ab-testing.php some path variables are setup using the string "wp-content".
This sets up the path variable incorrectly in my WP project because my content folder is not called "wp-content". WordPress not only allows you to move the wp-content folder but also rename it to whatever you want. That's why it's best to rely on the WP helper functions relating to the plugin directory path.