That simply means that you have been assigned the same ip address as someone else.

Since an ip address tells every other computer out there where you are and how to get traffic back to your machine, you can only have one of them on a network.

Unless you are on a private network... private ip addresses are not routable... but that is a whole other story.

If you are on a private lan, choose a different ip address that is not in use.

If you are recieving this on the internet... then contact your ISP.

A little more info about your network setup and or setup in general would be useful.