Unable to customize Sydney Theme

Whenever I click customize, this comes https://www.dropbox.com/s/fetifxrtk1h9efv/Screenshot%202017-01-09%2018.57.52.png?dl=0

What can I do to fix this ASAP?

Hello ShanShan,

It looks like file permissions issue. Please check these topics:
https://wordpress.org/support/topic/error-the-theme-directory-child-does-not-exist/
https://wordpress.org/support/topic/the-theme-directory-does-not-exist/

Please feel free to ask any other questions that you might have.

Kind Regards, Roman.

Kindly check the plugins. You have installed incompatible plugin. Woocommerce sometimes cause that.