DNS Servers

DNS (domain name system) servers are computers on the Internet that interpret Web addresses and turn them into IP addresses, such as 192.168.0.1.

DNS error defined

A DNS error occurs when your Web browser can't reach a valid DNS server and can't translate Web addresses. The result is that the Web page you're trying to reach can't be displayed in your browser.

Connected to the Internet

A DNS error may mean that you're not connected to the Internet. If you get a DNS error message in your Web browser, try connecting to the Internet via your email or chat program. If you can't connect, troubleshoot your connection.

DNS Down

If you have a working Internet connection but can't reach websites, your DNS server may be down. When your PC or Mac is configured to connect to the Internet, it's generally configured to connect to your Internet service provider's DNS servers. If those servers are unavailable, you may see this error. Contact your ISP for support.

Internet Explorer and DNS errors

Microsoft's Internet Explorer is known to display a general DNS error that can result from Windows configuration problems. If you're connected to the Internet and can't connect to certain sites in Explorer, you may need to contact Microsoft's support crew or use a different computer to access Microsoft's Answers website and search for "DNS error." (You can also use a third-party application such as PageFix to solve some DNS errors in Explorer.)

Source:

Microsoft Answers

DNS Error in IE 7