The function "crm_create_activity" calls "_crm_check_activity_name( $activityName, 'CRM_Core_DAO_ActivityType' );", but CRM/Core/DAO/ActivityType.php does not exist, causing a PHP error.
I think the following is what would be necessary:
crm_check_activity_name( $activityName, 'CRM_Activity_DAO' . $activityName ); // first param becomes useless
This bug also affects the update/delete API calls.