What do you mean by "no longer work"?
Go to the design studio, check they are here.
Then select one of them, you will find the URL you should use to access it.
looks like a dns issue for you. Your machine is failing the lookup for the pages.getwirelessllc.com domain, so you're getting that message. I get this result for nslookup from my local:
pages.getwirelessllc.com canonical name = getwireless.mktoweb.com.
That's what you should expect to see for the domain lookup. I would ask your IT department about this, since it looks like a local problem for you.
What happens if you try to go to the URL for one of your landing pages, your Unsubscribe page, for instance? If it's giving you Page Not Found, then you are probably lacking a CNAME entry on your internal DNS. You can doublecheck this by trying to access the page using an external network such as your smart phone's carrier network. The solution is to have the CNAME record for pages.getwirelessllc.com copied onto your internal DNS.