I can't speak to your particular case, but my ticketmaster transactions often fail to complete for various reasons. After one falls through, if I wish to purchase the same seats again, they're often unavailable. This isn't because some scalper swooped in and bought them, the person who has dibs on them is me, in my previous defunct transaction. I usually find that if I wait ~ 15 minutes the hold will be released, and the tickets will be available for me to try again.