403 error with iCal CalDAV client when inviting contacts

[valentinwizzgo]

Hi,

I have a very strange problem using ZCS 5.0.9 OSE with Apple iCal (CalDAV Client).

The user's calendar is defined in iCal, everything works (read and write). There is only one very strange issue :

when an user (userA) want ton invite a contact (userB), he adds him to the invite list, the Free/Busy feature is OK, but when he want to save, it doesn't work : the spin wheel (progress indicator) turns for ever.

After analysing network traffic, this request fails with 403 :

**********************
POST /dav/userA/Sent/ HTTP/1.1
Authorization: Basic HIDDENAUTHKEY==
Recipient: mailto:userB@company.com
Content-Type: text/calendar
Originator: mailto:userA@company.com
Content-Length: xxxx
Connection: keep-alive
Host: zcs.company.com

<<< SNIPPED CALENDAR DATA >>>
**********************

This is confirmed viewing Zimbra-Jetty's log :
192.168.0.222 - - [08/Sep/2008:19:48:30 +0200] "POST /dav/userA/Sent/ HTTP/1.1" 403 0 "-" "DAVKit/2.0 (10.5.4; wrbt) iCal 3.0.4"

Does someone encounter the same issue ? Is there a way to analyse more precisely what's the matter ?

Thanks in advance,
Valentin