When you look at a sweeps page you should see a green button that says "Add to Lucky List". When you click that it adds it to your lucky list and if your browser is working properly it will turn the button red and change it to say "Remove from Lucky List". If you're talking about the red "Enter" button on your lucky list page next to each sweep, when you click it, it should open another tab or window with that sweep in it, and change the button from red to green (some browsers don't play nice and don't do that, simply refresh the page and it'll change colors).

I had same problem in IE, switched to Chrome and it works for me now.