To replicate, please go to sign up and when you press through to the next step, you will get a blank page with an error.
The error is "Error 324 (net::ERR_EMPTY_RESPONSE): The server closed the connection without sending any data."
I have re-uploaded all of the Xenforo files so I can only assume it's a server issue.
My hosting company was able to replicate this problem too. One of my team was able to register though and thought that it may have been a caching issue.