It's probably a conflict of NAT types. If your NAT is open it doesn't matter. If you're NAT is moderate you'll have problems connecting to other people who have a moderate or strict NAT type. It's even worse with Strict.
Adjusting the netcode isn't going to change that. You need to open your NAT type. You can do so by going into your routers config from your web browser.
It's probably a conflict of NAT types. If your NAT is open it doesn't matter. If you're NAT is moderate you'll have problems connecting to other people who have a moderate or strict NAT type. It's even worse with Strict.
Adjusting the netcode isn't going to change that. You need to open your NAT type. You can do so by going into your routers config from your web browser.
Exactly what I was going to write. This is your problem right here. There's videos all over YouTube with instructions on how to open your NAT type. If you're clueless on how to deal with your router setting and such, it can be a bit challenging. If all else fails maybe try calling your router or cable company for assistance.
I had to change mine a while back when GTA IV wasn't letting me in most games. Once I changed it, I've never had that problem again.