You had to register with them and have an ID in order to purchase a ticket (very different than previous years). Also please note that a Comic Con ticket buys you access to the Convention Hall, not a guaranteed admission into any specific panel or presentation. For that reason it’s first come first serve and sometimes sleeping outside for days at a time is required.
Please also note that though the Twilight films have typically been at Comic Con on a Thursday, there is no guarantee that will happen again. It’s up to the Comic Con staff who do the scheduling and now Lionsgate to bring them there. Do we think they will be there? Yes! We’re betting on it. Are we sure on the day? No. Especially since the same studio now has Twilight and The Hunger Games who knows what they will want to do to maximize that PR. It’s also probably worthwhile to note that almost no movie or TV outlet has confirmed their presence at Comic Con at this point, nor will anyone have anything specific about dates(under Comic Con not studio control) until a month or so out.
If you did follow the procedure and preregister and have an ID you ABSOLUTELY NEED TO READ THIS DOCUMENT! Yes it’s long but trust us you want to read it. It covers the finer points on how the registration system work and what to expect in regards to wait time, what browsers to use, what email addresses work best, etc. http://www.comic-con.org/cci/reg/cci12_helpfulhints.pdf
As this article in the LA Times notes, last year the ticketing system went down several times and when they finally resurrected it, it sold out in 24 hours. So, even if the wait is long, you want to login to get your tickets on the first day, or there will likely not be any left.