So I have a few users that are experiencing this problem, and I have just tested it on my account and it is happening to me too. We have recently upgraded to ZD 7.1.2 build 10978 and this was not a problem with ZD 2. So here goes, create a new Local Folders Calendar, nothing special, just plain jane calendar in my local folders. Then try to add an appointment to that calendar, or any local folders calendar for that matter and we get a the following error:
Item "581" does not exist.
method: [unknown]
msg: no such item: 581
code: mail.NO_SUCH_ITEM
detail: soap:Sender
trace: com.zimbra.cs.mailbox.MailServiceException$NoSuchI temException: no such item: 581 ExceptionId:btpool0-24:1324308461995:c9343bd69d006bb0 Code:mail.NO_SUCH_ITEM ArgitemId, IID, "581") at com.zimbra.cs.mailbox.MailServiceException.NO_SUCH _ITEM(MailServiceException.java:157) at com.zimbra.cs.mailbox.MailItem.noSuchItem(MailItem .java:1318) at com.zimbra.cs.db.DbMailItem.getById(DbMailItem.jav a:2288) at com.zimbra.cs.mailbox.MailItem.getById(MailItem.ja va:1251) at com.zimbra.cs.mailbox.MailItem.getById(MailItem.ja va:1247) at com.zimbra.cs.mailbox.Mailbox.getItemById(Mailbox. java:2095) at com.zimbra.cs.mailbox.Mailbox.getItemById(Mailbox. java:2066) at com.zimbra.cs.mailbox.ZcsMailbox.getRenumberedItem ById(ZcsMailbox.java:254) at com.zimbra.cs.mailbox.ZcsMailbox.getItemById(ZcsMa ilbox.java:240) at com.zimbra.cs.mailbox.Mailbox.getItemById(Mailbox. java:2057) at com.zimbra.cs.service.mail.MailDocumentHandler.get ProxyTarget(MailDocumentHandler.java:69) at com.zimbra.cs.service.mail.MailDocumentHandler.pro xyIfNecessary(MailDocumentHandler.java:51) at com.zimbra.soap.SoapEngine.dispatchRequest(SoapEng ine.java:403) at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:287) at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:158) at com.zimbra.soap.SoapServlet.doWork(SoapServlet.jav a:294) at com.zimbra.soap.SoapServlet.doPost(SoapServlet.jav a:215) at javax.servlet.http.HttpServlet.service(HttpServlet .java:725) at com.zimbra.cs.servlet.ZimbraServlet.service(Zimbra Servlet.java:208) at javax.servlet.http.HttpServlet.service(HttpServlet .java:814) at org.mortbay.jetty.servlet.ServletHolder.handle(Ser vletHolder.java:511) at org.mortbay.jetty.servlet.ServletHandler.handle(Se rvletHandler.java:390) at org.mortbay.jetty.security.SecurityHandler.handle( SecurityHandler.java:218) at org.mortbay.jetty.servlet.SessionHandler.handle(Se ssionHandler.java:182) at org.mortbay.jetty.handler.ContextHandler.handle(Co ntextHandler.java:765) at org.mortbay.jetty.webapp.WebAppContext.handle(WebA ppContext.java:422) at org.mortbay.jetty.handler.ContextHandlerCollection .handle(ContextHandlerCollection.java:230) at org.mortbay.jetty.handler.HandlerCollection.handle (HandlerCollection.java:114) at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:152) at org.mortbay.jetty.handler.rewrite.RewriteHandler.h andle(RewriteHandler.java:230) at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:152) at org.mortbay.jetty.Server.handle(Server.java:326) at org.mortbay.jetty.HttpConnection.handleRequest(Htt pConnection.java:543) at org.mortbay.jetty.HttpConnection$RequestHandler.co ntent(HttpConnection.java:946) at org.mortbay.jetty.HttpParser.parseNext(HttpParser. java:756) at org.mortbay.jetty.HttpParser.parseAvailable(HttpPa rser.java:218) at org.mortbay.jetty.HttpConnection.handle(HttpConnec tion.java:405) at org.mortbay.io.nio.SelectChannelEndPoint.run(Selec tChannelEndPoint.java:410) at org.mortbay.thread.BoundedThreadPool$PoolThread.ru n(BoundedThreadPool.java:451)

The item exists, because I just created it. This used to work prior to version 7, I had one user using it extensively and now cannot add appointments to the local folders calendar.