I am running a few instances of 5.0.1 NE, all on Ubuntu. I can't get the Mac OSX 10.5 (Leopard) iCal use CalDav against the Zimbras. I tried to use the instructions in CalDAV with Leopard iCal - Zimbra :: Wiki, but that doesn't work. I get the "Account information not found - Request encountered an unexpected error (domain (null)/code 0)." bug as described in Bug 23821 - iCal unable to subscribe to CalDAV account
Anyone that did get it to work using firstname.lastname@example.org logins instead of "short" user logins?