Have reviewed your install and the call backs for version checking fail, your ajax checks for email and username fail, I believe something is not configured appropriately on your host. I can't say as to what as I don't know how your host runs their servers. Please contact them in regards to reviewing the mailserver logs to see if emails are even reaching the mail server and if they are what errors are presented. Your host is also using PHP5.2, if possible please contact them to upgrade to PHP5.3 and confirm if issue still present.