After some tests last week I decided to install Zimbra on the production server.
Now that everything appeared to be ok, when I log in the user using the AJAX desktop (not standard html) it FREEZES completely the browser. The only solution is to kill the browser, and this is not a browser problem because IE, Firefox and Epiphany have the same problem, in linux and in windows.
Also I tried in the local machine where Zimbra is and the same.

The situation occours not at the beginning of the load of the page but I would say by the end.

The standard html works fine.

Any suggestions please