Remember the Smith Barney commercial with John Housman? In it he says, "They make money the old fashioned way - they earn it."
Well, it's the same thing with your network. We build our networks for many reasons, one of which is asking for favors. It can be a referral, maybe a recommendation. Perhaps you need a job or want someone to buy your book.
Before asking for anything - you must get to know the other person, and have them get to know you. You need be to the point where you've earned their trust. That's when people want to help.
So, please don't ask a favor when you've barely met someone. Networking is hard work, and you get the rewards the old fashioned way - you have to earn it.