I too had this error for ages. none of the resets worked etc. FINALLY i was able to work out what to do. Turning off the router/modem etc does not flush all the old settings out so the router just reverts back to what it was doing. I had to perform a hard reset and, depending on your router, the way to do it is to find the reset button (mine was recessed and I had to use a pen or paperclip) and hold it in for more than a minute. Just to be sure I held it in for a minute with the power on, then turned the power off (still holding it in) and turned the power back on and then released the button. My network then found the router as if it was a totally new part of the network and I could get my PS3 to automatically find it and use auto settings.

It worked for me, now I have my PS3, PSP, laptop and everything running smooth...

I hope that helped.