During the installation process the installation manager checks the license file is correct/valid against episerver website.
So make sure the manager can access the internet - or do an offline installation.
Which version of episerver cms is it btw?
I am trying to install Episerver CMS 5.
Also when we try to install it offline, it displays the error message as
"Error Validating license: 10.227.14.18 is not a valid IP Address (Check your License file)"
This is the IP address which I had typed while registering myself with Episerver website.