Using thunderbird and lightning 0.3.1. When updating a calendar that has been shared we are getting a 500 internal server error, the cause of which is attached from mailbox.log. On unshared calendars, this does not occur and updating the calendar works beautifully. This error occurs both when authenticated as the owner of the calendar, as well as one of the users with shared access.

PHP Code:
2007-06-04 20:04:09,799 INFO  [http-80-Processor93] [mid=8;ip=71.190.65.254;name=user@domain.dom;] mailbox UserServlet (POST): http://zimbra.domain.dom/service/home/user@domain.dom/calendar
2007-06-04 20:04:09,933 ERROR [http-80-Processor93] [] [UserServlet] - Servlet.service() for servlet UserServlet threw exception
com
.zimbra.common.service.ServiceExceptioninvalid requestChanging organizer of an appointment/task is not allowedold=user@domain.dom, new=:otheruser@domain.dom":MAILTO:user@domain.dom
        at com.zimbra.common.service.ServiceException.INVALID_REQUEST(ServiceException.java:182)
        at com.zimbra.cs.mailbox.CalendarItem.processNewInviteRequestOrCancel(CalendarItem.java:638)
        at com.zimbra.cs.mailbox.CalendarItem.processNewInvite(CalendarItem.java:601)
        at com.zimbra.cs.mailbox.CalendarItem.processNewInvite(CalendarItem.java:574)
        at com.zimbra.cs.mailbox.Mailbox.addInvite(Mailbox.java:3112)
        at com.zimbra.cs.service.formatter.IcsFormatter.saveCallback(IcsFormatter.java:134)
        at com.zimbra.cs.service.formatter.Formatter
$SaveOperation.callback(Formatter.java:273)
        at com.zimbra.cs.operation.Operation.schedule(Operation.java:190)
        at com.zimbra.cs.service.formatter.Formatter.save(Formatter.java:103)
        at com.zimbra.cs.service.UserServlet.doPost(UserServlet.java:438)
        at com.zimbra.cs.service.UserServlet.doPut(UserServlet.java:376)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:712)
        at com.zimbra.cs.servlet.ZimbraServlet.service(ZimbraServlet.java:162)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
        at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:672)
        at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:463)
        at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:398)
        at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:301)
        at com.zimbra.webClient.filters.SetHeaderFilter.doFilter(SetHeaderFilter.java:286)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
        at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:541)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
        at org.apache.coyote.http11.Http11BaseProtocol
$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:667)
        at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
        at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
        at org.apache.tomcat.util.threads.ThreadPool
$ControlRunnable.run(ThreadPool.java:684)
        at java.lang.Thread.run(Thread.java:595)