If wireless switch to wired see if it works if not then your going to need to place your router into DMZ
Get your Portable ID!
By the way, this is a PS3 network issue. Mine started with signing me out frequently but I can immediately sign back in. Just can't play multiplayer. I'm wired connected to modem and it happens only to my PS3 and no other device I own(not the 360, pc, wii, and a mac which I connect to modem when needed). I thought it was my ISP but when the tech came over he also informed me that it happens to several of his customers and himself who also have the PS3. I receive no error code just a notice that I'm signed out of network. Just FYI. Probably will be fixed with an update later on is my guess.