Facebook Login Gives me an error

Usually, that happens when your testing with a brand new Facebook application. It should clear itself up in a few hours, but here's a few things that can work around the problem quicker:
1) Don't be logged into Facebook in another tab when initially testing
2) Shut down and restart your browser
3) Clear the cache of your browser
4) Try a different browser altogether

Hopefully one of those work, but if your application isn't new or this doesn't clear up soon, please post the URL of the page you're seeing it on, and we'll do what we can to get you fixed up.

Thanks,
Alex