iCal Feature, Bug, or I don’t know how to configure it?

We have a school calendar running on iCal Server (10.6.4) called "CS Calendars". Each user has one default calendar when the account is created on the local MacBook (10.6.4). Many users have created additional calendars under "CS Calendars" so that they will show up as "busy" if they schedule stuff on the other calendars. Here's the problem... A users sends an "invite" to another user. That user accepts the invite. The appointment shows up initially under "(username)'s Calendar" under "CS Calendars". The user now wants to change the appointment to another of their calendars under "CS Calendars". As soon as they select the other calendar an error message pops up saying: [b]The server responded with an error.[/b] The request for (Name of Invite) in (Name of OTHER Calendar) in account "CS Calendars" failed. The server responded with "HTTP/1.1 502 Bad Gateway" to operation CalDavMoveEntityQueueableOperatioin. I have googled that error operation and can't find but 6 links on the entire internet that has any reference to it and some of them are duplicates. Is this a prohibited operation by CalDAV? (The user SWEARS to me that she was able to do this last year - we have had 4 iterations of 10.6 since then) Is this a bug in CalDAV? or (more likely) Do I not have iCal Server configured correctly OR the client misconfigured. Thanks for any help. John Orban System Administrator The Country School