facebook C# sdk can't get authenticated

I can't get authenticated. I click the login button, I enter username and password, but still the FacebookWebcontext.Current is like this:

So what is the problem, why doesn't i开发者_如何学Got authenticate. is there a way to see what is the problem? What settings are wrong, or if facebook refused to issue the authentication for the app?

checkout the "samples" folder from the source code, for examples.