IP conflicting and another problem

About a year ago I replaced my cisco router with an AirPort Extreme. A few weeks ago in airport utility, t started saying that there was an IPv6 Relay Error. So I clicked edit, and it brought me to the internet options menu. I experimented, and found that when I set the IPv6 mode to native it didn't show an error(Before, I had set it to tunnel). I prefer it to be in tunnel mode, so can someone explain how to set it to tunnel without having an error!!! About the IP conflicts. It also started about when the other error stared. So, I was using my virtual machine, and it said "Window is having an IP conflict" or something like that... How can I fix this!!