Martin,Is this a new error? did you change any of the setttings? Has anything preceded this problem? You can give this a try. In the settings under network, disable Media Server and disable Auto Sign-in as well and see if that makes a difference. If that does not work at all for you, it could be that the IP address on your PS3 is wrong. That way your PS3 cannot connect via router to the internet, no matter what DNS you have configured. Set your PS3 to obtain the IP address and DNS server addresses automatically via DHCP from the router. You do not need to configure the OpenDNS servers explicitly on any connected devices, whether it be a computer, or PS3, or Wii, or iPhone, etc. I believe that there might also be issues that originate from the wireless controller, but I have not researched that possibility in depth.
There is plenty of info about this happening and I am sure it is not a hardware issue but a software setup problem. Check here and here as well Good Luck and I hope this works for you.