There are a few possibilities.
1. Someone else is using your key from a different ip address
2. Someone else in your house is using your key with a different name
3. You attempted to change your name in-game without using the main menu screen
Looking at the records, your key has been used by several different IPs but they are all in the same area. Check if your friends or relatives are using it.
You forgot the 4th senario. He's using someone elses code and wants you to kick them so he can play. I doubt that's it but, hey, you never know.
