Deregister the license key from old domain and register it on a new domain

Hello,
I have created a website for a client on a subdomain of my dev server (beach.berlingraphics.de). After I finished the work I duplicated the wordpress installation and reinstalled it on clients server. To change the registration I deregister the license key from my dev server and register it on the new one, but I always get the message "Purchase code already used. Please deregister purchase code and remove theme folder on: beach.berlingraphics.de" I have even delited the subdomain and all files on my dev server, but the error message is still the same.