5.0.6 NE // Ubuntu 6.06

We have a new shared calendar that went out to several people with manager access. The calender works fine in the default combined/individual view, but when a user tries to launch the shared calendar in a separate window it will come up fine for the current month, but if you try to advance it to the next month or change it's view, you get: (I'm adding the < >'s to protect the innocent)

no such item

RequestURI=/service/home/<user>/<shared calendar>.html

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The user does not have this problem with their own calendars, and the owner does not have this problem with the shared calendar, only the people who are sharing...

The URL that initially comes up with the current month in a separate window (and is ok to at least look at):

http://<FQDN>/home/<user>/<shared calendar>.html

But one you try to I guess pass some parameters, be it the next month, change of view,etc:

http://<FQDN>/home/<user>/<shared calendar>.html?view=month&fmt=html&date=20080823

you get the above error..

Any help would be appreciated, a small issue, but having converted this client from Outlook, it's turning into (for some reluctant users) "see this new fangled zimbra thing is crap!"