Singing Up Problem

Hi Everybody!
I have some strange problem which I can not recreate by myself. Some users reporting me that they have sing up problems. When they submit registration form they stuck in loading screen and I am getting what I use to say – empty email, New user registration on your site DailyQuest: Username: Email: .

For some of users I have to switch language back to English, but there is users without problems…. What is the problem?