I would be glad to help. The issue they are experiencing is a bad DNS server. They can fix the issue by changing the DNS server settings on their computer. I would ask them to follow the instructions on the linked page below. If that does not resolve the problem please let me know and I can look into alternative solutions.
If none of the DNS servers from the provided link are able to resolve the issue, I would ask them to also try using Google's DNS servers which are:
Please let me know if that was able to resolve the issue. If not it may be specific to the browser they are using. Please ask them which browsers they are using that are experiencing the problem if my DNS fix did not work.
Also, if they are having trouble following the instructions on that page, they may need to click the "Advanced..." button after opening the Network settings in order to see the TCP/IP and DNS settings. I hope that helps!