I'm trying to update a calendar invite using soap and php.

I sent:

Code:
<ModifyAppointmentRequest id="206297" comp="0" xmlns="urn:zimbraMail">
I got:

Code:
<Error xmlns="urn:zimbra">
<Code>mail.INVITE_OUT_OF_DATE</Code>
<Trace>com.zimbra.cs.mailbox.MailServiceException: The specified Invite is out of date (has been updated): e8713cab-6e90-4670-b499-e8efd12862d5:206297
at com.zimbra.cs.mailbox.MailServiceException.INVITE_OUT_OF_DATE(MailServiceException.java:351)
at com.zimbra.cs.service.mail.ModifyCalendarItem.handle(ModifyCalendarItem.java:102)
at com.zimbra.soap.SoapEngine.dispatchRequest(SoapEngine.java:270)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.java:168)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.java:90)
at com.zimbra.soap.SoapServlet.doPost(SoapServlet.java:223)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
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.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)
</Trace>
</Error>
Line 102 here: SourceForge.net Repository - [zimbra] View of /trunk/ZimbraServer/src/java/com/zimbra/cs/service/mail/ModifyCalendarItem.java

Says that it is probably something to do with compNum... which from my createAppointment returned:

Code:
<comp seq="0" transp="O" loc="location" fb="B" status="CONF" apptId="206297" isOrg="1" fba="B" calItemId="206297" compNum="0" rsvp="0" x_uid="25798dea-4f7f-4056-9979-b488d7003f03" name="Complete Job">
<s d="20071031T100000" tz="(GMT-05.00) Eastern Time (US &amp; Canada)"/>
0 = compnum

So what is it? What does it really mean? Help!? TIA.