"A Serial number could not be verified because of a temporary problem connecting to the server. Try again later, or continue installation without product entitlement information. You will still be able to choose the products you want to install, but you will not be able to download any installation files. If you continue without downloading enabled, you will need to provide a complete set of download source files or a DVD from which to install.
Click Back to check the serial number you entered or enter a new serial number. If you continue without a validated serial number, the Installation Manager will not pre-select the products to which you are entitled."
I tried registering that serial number on this website but I got error saying invalid serial number.