You need a valid license key for one click updates (Introduced in version 7.2.5) to work.
If you have an active license, you can get the activation key from the licenses tab in [members area http://swiftthemes.com/swiftlers-area/softsale/license].
After you get the activation key from members area, goto your WordPress dashboard -> Swift Activation ( Under swift options menu), enter your license key and click on validate license.
You can use personal license on 5 domain and developer license on 18 domains.
If you are a developer and don't want your client to see the license activation and renewal nags, then use I_DONT_WANT_ONE_CLICK_UPDATES as license key.