This comes up quite often, it's a known problem and not much can be done about it. Please read on.

The site doesn't have a unique identifier for every person (which is pretty dumb).

Somebody from the same ISP (and probably lives close to you) has already voted for EE or another game they play, making it impossible for anybody else in your area (on that ISP) to vote as well.

It's not something thats controlled from this side, you might want to try contacting them and voicing your opinion on the matter. http://www.top100arena.com/contact.asp