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?

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