www throwing an error

I have a multisite setup at https://sexyfitness.com, I have configured all of the DNS as recommended in the documentation.

If you go to https://www.sexyfitness.com/ you get a php error : “Notice: add_custom_background is deprecated since version 3.4! Use add_theme_support( ‘custom-background’, $args ) instead. in /home3/forwill/public_html/wp-includes/functions.php on line 3078”

We’re not using custom backgrounds in the new theme that we’re using. So I’m lost as to why this would throw an error, especially when i have the DNS configured to point www to sexyfitness.

Any ideas why this is happening.