Publish Post using Facebook API with iOS native App

Question

I integrated Facebook SDK into my iOS native APP. I completed login and received active FBSession. Then I ask for publish permission and then I want publish a new ost on my wall or on friend wall. I don't understand how to do it, can you help me please?

NSMutableDictionary<FBOpenGraphObject> *object = [FBGraphObject openGraphObjectForPost];
                            object.provisionedForPost = YES;
                            object[@"title"] = @"This is Test!";
                            object[@"image"] = @"http://www.test.com/myimage.png";
                            [FBRequestConnection startForPostOpenGraphObject:object
                                                           completionHandler:^(FBRequestConnection *connection, id result, NSError *error) {
                                                               if(error) {
                                                                   NSLog(@"Error: %@", error);
                                                               } else {
                                                                   NSLog(@"Success %@", result);

                                                               }
                                                           }];

I receive this error:

2013-09-07 12:50:36.078 LSFacebook[1177:c07] Error: Error Domain=com.facebook.sdk Code=5 "The operation couldn’t be completed. (com.facebook.sdk error 5.)" UserInfo=0xa24e730 {com.facebook.sdk:HTTPStatusCode=500, com.facebook.sdk:ParsedJSONResponseKey={
    body =     {
        error =         {
            code = 1;
            message = "An unknown error has occurred.";
            type = OAuthException;
        };
    };
    code = 500;
}, com.facebook.sdk:ErrorSessionKey=, expirationDate: 2013-11-06 10:29:13 +0000, refreshDate: 2013-09-07 10:50:25 +0000, attemptedRefreshDate: 0001-12-30 00:00:00 +0000, permissions:(
    installed,
    "basic_info",
    email,
    "publish_actions"
)>}

Thanks

Luca