If you're very unlucky, when you install Divi Booster you may be met with a "mkdir(): Permission denied" warning.

This is a result of the file permissions set on the /wp-content/uploads directory within your WordPress installation. Divi Booster needs the write permission to this folder, or it is not able to save the CSS and JavaScript files it creates (wp_head.css and wp_footer.js). If the server has been configured to deny write access to this directory, then Divi Booster will be unable to save its files and will generate the error above.

To fix this, please ensure that the /wp-content/uploads directory is writable. This can be done by setting the permissions level on the folder to 755 (or similar). You should be able to set the permissions on the folder using either an FTP program, through your web host file manager, or using a WordPress security plugin (you may already have a security plugin installed which is restricting the permissions in the first place).

For more information on file permissions within WordPress and how to change them, please see: Changing File Permissions