[Inf-IT DAVcl] Empty page with caldavzap

When I connect, to my https://davical.server/caldavzap/index.html the page seems empty. It is not and if I key in Enter key, login dialog appears, then calendars appear. But I can no more edit the calendar : add modify or delete event. The same problem appears with carddavmate. The same problem appears on other html clients, it is a server problem, not client problem. It has worked very fine during weeks, and I do not see what I may have changed on the server. In fact, I do not remind having changed something... Any tip? Thank you.