You need to trace through the step before it gets here i.e. where it calls the delegate in BooksManager.m

Specifically this is in the method below where book starts out as nil, and it will remain so if there is a problem.  Step through this to discover why it is nil.

N

-(void)infoDownloadDidFinishWithBookData:(NSData *)bookData withConnection:(NSURLConnection *)connection

{

    Book *book = nil;

    if (bookData)

    {

        //  Given a NSData, parse the book to a dictionary and then convert it into a Book object

        NSError *anError = nil;

        NSDictionary *bookDictionary = nil;

        //  Find out on runtime if the device can use NSJSONSerialization (iOS5 or later)

        NSString *className = @"NSJSONSerialization";

        Class class = NSClassFromString(className);

        if (!class)

        {

            //  Use custom BookDataParser.

            //

            //  IMPORTANT: BookDataParser is written to parse data specific to the Books

            //  sample application and is not designed to be used in other applications.

            bookDictionary = [BookDataParser parseData:bookData];

            NSLog(@"#DEBUG Using custom JSONBookParser");

        }

        else

        {

            //  Use native JSON parser, NSJSONSerialization

            bookDictionary = [NSJSONSerialization JSONObjectWithData: bookData

                                                             options: NSJSONReadingMutableContainers

                                                               error: &anError];

            NSLog(@"#DEBUG Using NSJSONSerialization");

        }

        if (!bookDictionary)

        {

            NSLog(@"#DEBUG Error parsing JSON: %@", anError);

        }

        else

        {

            book = [[[Book alloc] initWithDictionary:bookDictionary] autorelease];

        }

    }

    //  Inform the delegate that the request has completed

    [delegate infoRequestDidFinishForBook:book withTrackableID:[thisTrackable cStringUsingEncoding:NSASCIIStringEncoding] byCancelling:[self cancelNetworkOperation]];

// rest of code

}

yes i did and when detecting the marker it logs with 

Successfully created new trackable 'track name' with rating '4'.

-(void)infoRequestDidFinishForBook:(Book *)theBook withTrackableID:(const char*)trackable byCancelling:(BOOL)cancelled

{

    if (theBook) // nill 

    {

        trackingTextureAvailable = NO;

        [[ImagesManager sharedInstance] imageForBook:theBook

                                        withDelegate:self];

        NSLog(@"a     >>    %@",theBook.author);

        NSLog(@"b     >>    %@",theBook.bookURL);

        NSLog(@"c     >>    %f",theBook.listPrice);

        NSLog(@"d     >>    %@",theBook.listPriceString);

        NSLog(@"e     >>    %@",theBook.thumbnailURL);

        NSLog(@"f     >>    %@",theBook.title);

        NSLog(@"g     >>    %f",theBook.yourPrice);

        NSLog(@"h     >>    %@",theBook.targetID);     

    }

    else

    {     

        // so it get here 

        if (NO == cancelled)

        {    

            //  The trackable exists but it doesn't exist in our book database, so

            //  we'll mark that UniqueTargetId as a bad target

            [[BooksManager sharedInstance] addBadTargetId:trackable];

        }

         //  If theBook is nil, the loading UI would be shown forever and it

        //  won't scan again.  Send a notification to revert that state

        [[NSNotificationCenter defaultCenter] postNotificationName:@"kStopLoading" object:nil userInfo:nil];

    }

}