app credentials doesn't comes

Based upon the same question you asked here[^], I see that the error you are getting is "Object reference not set to an instance of an object". This error occurs when you do not properly instantiate a class object. For instance, if you have a class Foo and you want to assign it to a variable bar, this would not work:

Foo bar;
bar.Run();

Instead, you would see this same error (as long as this class exists). Instead, you need to instantiate the variable like this:

Foo bar = new Foo();
bar.Run();

Somewhere in your code, you are using a class reference without first instantiating it. If you identify which variable it is griping about, you will find your answer.

My recommendation would be to take the code from the article you referenced and try to get the demo working. Once it is working, then try to recreate it (not something new - the same thing). Once that works, try implementing this code in your application. Along the way, you are going to see where you deviated from what the author did.

Update
For the actual Facebook data, I believe you are bumping against the need for extended Facebook permissions. Facebook doesn't give you access to all the data you can see on the screen via API without extended permissions. You will need to register your application and ask people for access to their data. Here is a link with more information:

http://developers.facebook.com/docs/authentication/permissions/[^]