It sounds like Javascript or some component that the AJAX (Regular) SmartZone needs to run properly is being blocked.
What you can do is while you are on the loading screen, make a note of the URL - specifically, the beginning part. (For instance, my SmartZone URL is http://sz0004.wc.mail.comcast.net/zimbra/mail#1 - so the SZ e-mail server that I am assigned to is sz0004.wc).
Next, while you are stuck on the loading screen, key in the following URL that corresponds to the SZ server that you are assigned to:
http://sz0004.wc.mail.comcast.net/zimbra/h/search
(You should just be able to backspace to the slash after the zimbra and type in the h/search.)
This will get you into SmartZone Lite. At this point, go to Preferences > General and set it to SZ Lite so you will always get into SmartZone Lite at logon.
SmartZone Lite is an HTML-driven web app like the old Webmail was. If you were able to get into the old Webmail system before on your computer, you should be able to get into SZ Lite. If you are going to be accessing it a lot from this computer, I'd just leave it on SZ Lite in Preferences.
JR
