If you cannot activate your account using a valid serial number and the internet is not blocked and the returned error message is that "sorry, there is a problem with your account".
You will get this error message if you try and give the same 'friendly name' to two different installations. Each installation needs to have a unique name. To get around this, either do not give a friendly name at the point of activating the software, and let it pick up the default, machine name - which will always be unique - or make sure that you do not give identical friendly names to two different installations.