If the site tells you that you are a "bot" it means it thinks you're not really a person. It's guessing that because of how you're logging in. There are a couple things that you might be doing to make the site think you're not real.
Make sure to check the "I'm not a robot" box and that it stays checked. This security measure is provided by Google, and it tries to get to know you as you log in to this and other websites. Once you've done it here and other places enough, it will leave you alone and all you have to do is check the box. Until then, it will ask you to do some photo matching and puzzle solving, things that non-people have a hard time doing. The box must be checked when you try to log in, or it will say you are a bot.
Make sure you wait long enough after clicking "Log In." If you double-click the log in button or if you click it again while it's processing, it will think that you are not a person because you didn't wait for the next page to load. This often happens on a cell phone because it's difficult to see the tiny progress bar in a cell phone browser. Click the button, and wait a little bit, watching for signs in your browser that it's working on logging you in, and don't click the button again.