Have you tried this yet?
Yahoo! Zimbra Desktop FAQ - Zimbra :: Wiki
* System is misconfigured and localhost can't be resolved. - Many Mac OS computers have this issue. If you are on Mac OS, try the following steps:
1. Make sure localhost is resolved to 127.0.0.1 on this computer.
2. Make sure your computer has a name. You can set that under System Preferences -> Sharing. Also make sure computers on your network can access your computer at <computername>.local.
3. If it still fails, the last resort is to change the binding of the back end server from localhost (loopback) interface to all interfaces. Open the config file <install>/jetty/etc/jetty.xml with a text editor and remove the line <Set name="host">localhost</Set>. Save the file and then restart the back end server