DNS errors generally occur when the IP address for a typed domain name cannot be found. This may happen when the server speed is too slow, so the time taken to find the IP address lapses. This is a general problem faced by those who access the Internet with a modem.
This is because dial-up speed varies in accordance with traffic, sometimes even disconnecting one from the Internet. This is not to say that it does not occur in the case of broadband connectivity. It can happen also in case of a broadband server problem.
You may also come across DNS errors if the website you are searching for is disconnected, since it is going through some construction process or upgrading process. At that point, the website owner requests the hosts to switch them off from the server in order to curtail traffic until the site is uploaded again.
DNS errors also occur when you misspell the domain name. In such a situation, even if a single letter is missing or added, it will not connect to the IP address and you will not gain access to the website. This is also the case for sending out emails. Any error in an email address makes the email bounce back to the sender.
DNS errors mainly occur due to typing faults. Thus, it is essential to be extremely careful when typing in domain names; otherwise you could be wasting a lot of time trying to access the site. Ideally, you should not keep complicated domain names, or visitors to your site may get confused and never reach you.