You get this error when trying to download updates, games or media. I got it when trying to update my trophy info after doing a system restore. It is to do with your network.
Some people as a temporary fix download the updates on their pc to a memory stick and transfer like that. I fixed the error on mine by doing this:
Go to network settings -> Media Server -> Off
That should work for most, others may require an update of firmware on the ps3 or router or both!