[sam]

Looks like your server is configured to run under the "/" instead of "/zimbra"

ie this is where the image is:
http://<your-server>/skins/_base/logos/LoginBanner.png

but the skin and login page think its under
http://<your-server>/zimbra/skins/_base/logos/LoginBanner.png

also, this url doesn't load the app:
http://<your-server>/zimbra/

Im guessing its a config issue, but could be a bug with zimbraMailURL & skins. Check this bug for more info:

Bug 30114 &ndash; zimbraMailURL not called in jetty.xml.in