1) Start Installer
2) Start Setup Factory Helper as an administrator.
3) Continue with Installer and at serial number screen, press 'Retrieve' in Setup Helper - serial hashes will follow.
4) Double click on serial hash (any you want) in Helper.
5) In dialog box that pop up enter, now use any serial you like and write that serial in Text field.
7) Press Replace.
8) Copy serial you put in Text entry and paste in Installer Serial Number box.
9) Continue with installing.