iphone facebook session failing. why?

I'm learning how to integrate facebook api in iphone app. First I visited facebook website, went to applications->developer and created an app. Noted down private key and secret key. Now, I'm using FBConnect sample code. I am using my keys in FBConnect app. And I set session proxy as

static NSString* kGetSessionProxy = @"SessionViewController"; // @"<YOUR SESSION CALLBACK)>";

I'm able to run the app and when I click "Connect to Facebook", its asking me for credentials as well. But afte providing credentials, its failing. The following delegate method is being called:

- (void)sessionDidNotLogin:(FBSession*)session { _label.text = @"Canceled login"; }

I'm not understanding why I'm ending up 开发者_运维问答in above delegate.

What are all options that I've to select in facebook website when creating new application?

Please help me.

When I made kGetSessionProxy to nil, it worked without any problem. But I didn't understand why it didn't when i gave some value.