I have a DNS Error

I have a DNS Error all the time while playing Metal Gear Solid 4 for the PS3. Sometimes that message would pop up then sign me out of the Playstation network. Other times I would get disconnected from the host and also get signed out of the PS Network, and sometimes too a message would say communication servor error. These problems only happen on that particular game. Sometimes I get disconnected from online play on other games but usually that can be fixed. I really want to play this game so badly. Please help me out, i would appreciate it.