Stuck un registration page

[ilfungo]

Hi many of my customers say the registration module doesn't go on when clicking the button on registration page without reporting any message. I have no idea of why and what to do to solve the problem as I never experienced the same problem. They say all the fields are complete. I suddenly ask for browser and OS and mainly they have win7 and IE 11, if they have another browser I ask to try from another browser but they complain the same result. I try a test from my ie11 from my windows 7 and nothing go wrong. This the main shop page: http://www.aispiemonte.it/corsi/corsi-delle-delegazioni.html