@ porter, rot is right, you need to confirm their device is actually sending traffic through open dns. What is your network setup? Devices that are bypassing? More detail of the issue would be useful for troubleshooting.  Remember, if you don't have ...

Just as rotblitz said, this means the site you are trying to access is being blocked by your opendns settings. The browser is doing exactly as intended by raising an alarm (it is expecting one site, but getting the certificate for another one, in thi...