Upgrade error: Cannot redeclare wp_convert_bytes_to_hr()

When upgrading from 3.5.x to 3.6 using the wordpress update function you might experience the error Cannot redeclare wp_convert_bytes_to_hr() (previously declared in /xx/xx/xx/xx.com/public_html/wp-includes/deprecated.php:3364) after the update seemed to take ages.

This problem can be the result of an exotic variety of causes, mainly attributed to the setup of your server or issues with permissions. The use of 3rd party installation tools (such as installatron) can sometimes alter the installation process, standard foldernames or permission settings, and so on and so forth.

In the case you have access to your installation via FTP however, this issue can be solved quite easily in most cases. Simply grab the last copy of the wordpress installation from www.remarpro.com (currently 3.6 / oscar) and copy all files from the zip file except the wp-content folder and wp-config-sample.php and overwrite your current installation files. When you access your site after the overwrite, a database update might present itself when you view your website. Just role with it and you should be in the clear. All content and database info will remain intact.