Trying Zimbra. Zimbra desktop calendar invites not showing on mail or calendar

[cbarreda]

Server
Ubuntu Server 8.40 32 bit
zcs-NETWORK-7.1.3_GA_3346.UBUNTU8.20110928134609.tgz
Client
XP and Ubuntu 11
Account type Zimbra.
J (on Ubuntu) has invited C (on XP) to a meeting on Jan 17 2012 from 10:00 to 10:30 am.
C is not getting e-mail notification or 'calendar' notification.
C does not see on his calendar that he is scheduled to a meeting.
If C tries to schedule J then C can see J is busy 10 to 10:30

How do I fix?