This message will appear when attempting to activate a key code that has already been associated with another Steam account. The code can only be associated with one Steam account. Make sure that you are logging into the correct Steam account when the installer launches Steam. If you are sure that you are logging into the correct Steam account then please contact customer support. We will do our best to resolve it for you, however it may be necessary for you to contact Steam support in order to re-obtain your original account information.