It means what it says really, your PlaneShift client is out of date. You should use the PlaneShift Updater(updater.exe) to download the updated files. When you start the updating process it will first download a new version of the updater and install that, after that is completed you will have to start the updater again, and this time the process will download the new client and other files that has been changed since your current version. After the process is completed you can try again to log in the client.
