Hello, I succesfully upgraded Zimbra server (5->6).
Now, I have got Zimbra Desktop error on all our linux desktops (with Ubuntu 9.10).
I tried all last three versions Zimbra Desktop. The last one is not working at all.
Users of linux desktop must use web interface now.
(Widnows version of Zimbra Desktop works fine in the last version :'-()
Any help is welcome. Thank You!

Failure communicating with remote server. Please try again later.Debug message: invalid request: missing required attribute: n
Exception:
com.zimbra.common.service.ServiceException: invalid request: missing required attribute: n
ExceptionId:mid=2:1266926759586:06651abb25cea915
Code:service.INVALID_REQUEST
at com.zimbra.common.service.ServiceException.INVALID _REQUEST(ServiceException.java:260)
at com.zimbra.common.soap.Element.checkNull(Element.j ava:240)
at com.zimbra.common.soap.Element.getAttribute(Elemen t.java:208)
at com.zimbra.cs.mailbox.InitialSync.syncContact(Init ialSync.java:838)
at com.zimbra.cs.mailbox.DeltaSync.deltaSync(DeltaSyn c.java:270)
at com.zimbra.cs.mailbox.DeltaSync.sync(DeltaSync.jav a:92)
at com.zimbra.cs.mailbox.DeltaSync.sync(DeltaSync.jav a:76)
at com.zimbra.cs.mailbox.MailboxSync.sync(MailboxSync .java:188)
at com.zimbra.cs.mailbox.OfflineMailbox.sync(OfflineM ailbox.java:140)
at com.zimbra.cs.mailbox.OfflineMailbox.syncOnTimer(O fflineMailbox.java:121)
at com.zimbra.cs.mailbox.DesktopMailbox$1.run(Desktop Mailbox.java:436)
at java.util.TimerThread.mainLoop(Unknown Source)
at java.util.TimerThread.run(Unknown Source)
If issue persists please post description and debug information here.