Why can't i surf the web with Tor enabled?

I got the Tor internet privacy add-on for firefox, but whenever I have it enabled and I try to open a site or search, I get this message:

The proxy server is refusing connections. Check the proxy settings to make sure that they are correct. Contact your network administrator to make sure the proxy server is working.

What does this mean, and how do I fix it?

Tor requires a local proxy server (I believe the current one they are distributing in the tor bundle is polipo) to be running on your machine in order to actually proxy your http requests.

Either polipo isn't installed or it's not configured properly. I would try uninstalling and then reinstalling the latest version of the complete tor package (including polipo and the browser plugin) to see if that works.