Avoid "Request Denied by Wolfram|Alpha server (3004)" in free-form input?

Hello, just received my book “Hands-On Start to Wolfram Mathematica”, I’m trying to use the free-form on mathematica version 8, but when I type something like

= "plot sin(x)"

I get the message: Request Denied by Wolfram|Alpha server (3004)? what’s going on?