DENIC (.de registry) has changed the rules to transfer a .de domain name. From February 1st, an authorisation key (auth key) will be required in order to transfer a .de name. Your current registrar needs to provide you this code.
Up until now, all you had to do, when you wanted to transfer a .de name, was inform your current registrar about your wish to transfer your domain name. This was neccessary since your current registrar had to approve the transfer explicitly. This won’t be needed any longer. Once you have passed the auth key to your new registrar, the transfer will be completed shortly after.