This is happening either because the license key is expired or it is not activated on the URL the extension is installed on. This can sometimes happen if you install the plugin and activate the license key on a temporary URL and then update the site to the final URL.
To resolve the problem, log into your account, go to page “Account”->”License Keys”, then click on the “Manage Sites” link for the license key. From that page, you will be able to add or remove URLs for the license. Once the proper URL is registered on the license key, you will be able to install the update.