I can't think of anything useful, apart from the usual stuff, like making sure your email matches the one you enter into the confirmation line.
Not much info to go on.
Do you get a specific error message? Do you have any other email adresses you could try?
Also, I'm all signed up now, yay me!
I'm planning on catching a monday flight to the US, flying back to germany the monday after flite fest.
Since that gives me a few extra days.. are there any spots to visit in the area? Aerospace museums and the like would probably be high on my list.