The meaning of that message is that someone else has/shares the same IP as the one that you have, this exists to prevent people from cheating by making alts. You won't get banned for that, you just cannot enter the same raffle as someone else on your IP already has.

If you know someone in your house is also entering raffles you can apply for IP whitelisting in our forums: http://forum.scrap.tf/index.php?/forum/27-raffles-ip-whitelisting/

Please make sure to read the stickied guidelines on IP whitelisting in the forum!