Ticketmaster and other major outlets have built-in security to prevent people (and computers) from attempting to snarf up huge lots of tickets. It helps prevent scalpers and re-sellers from doing what they do. Their computers log every IP that hits their site, and when it sees too many for the same show.. BAM! You're locked out Automatically. Depending on the show and the particular site, it could be temporary or permanent. Hitting the site 50 times is A LOT. Their systems do a pretty good job at giving up the best available seats. You may have put yoursel back a few rows because of the time you took to keep hitting.
Solution: Use a different computer, or call the permanent blocker and explain you weren't trying to snarf, just trying for primo seats. If you get a real (sympathetic) person, they may unblock you, but there's no guarantee.
Super solution: 3 tries, buy your seats!