Considering they have a huge ad on their front page, and have been advertising like crazy, it does not surprise me that you can't get through. Coupled with the insane Wicked popularity that has swept this country (something I still don't get, but I digress), it could very well be that too many people are on the website right now.
I suggest waiting a bit, or maybe going down to the box office in person if you are in town. However, I know people who became members just so they could get these tickets before they went on sale (non-Broadway freaks, even), and they had slim pickings in the first and second tiers.
Its crazy, I know. I like Wicked, saw it a few times with the OBC, but have no intention of adding to this mania. Hope you can get through today and can get something!
"Why do you care what people might say? Why try to fit into their design?" (Side Show)