I'm having errors with connecting to Zimbra NE (latest, can't remember version). I can manually sync, and occasionally it seesm to sync itself, but

Is there any way I can fix this?

I always get the following error:

Code:
Failure communicating with remote server. Please try again later.  (debug info)

Debug message: cannot modify immutable object: 645

Exception:

com.zimbra.common.soap.SoapFaultException: cannot modify immutable object: 645
ExceptionId:btpool0-10:1240522086181:6cec454d9f0912ab
Code:mail.IMMUTABLE_OBJECT
	at com.zimbra.common.soap.Soap12Protocol.soapFault(Soap12Protocol.java:88)
	at com.zimbra.common.soap.SoapTransport.extractBodyElement(SoapTransport.java:263)
	at com.zimbra.common.soap.SoapTransport.parseSoapResponse(SoapTransport.java:224)
	at com.zimbra.common.soap.SoapHttpTransport.invoke(SoapHttpTransport.java:277)
	at com.zimbra.common.soap.SoapHttpTransport.invoke(SoapHttpTransport.java:226)
	at com.zimbra.common.soap.SoapTransport.invoke(SoapTransport.java:315)
	at com.zimbra.common.soap.SoapTransport.invokeWithoutSession(SoapTransport.java:302)
	at com.zimbra.cs.mailbox.OfflineMailbox.sendRequest(OfflineMailbox.java:776)
	at com.zimbra.cs.mailbox.OfflineMailbox.sendRequest(OfflineMailbox.java:740)
	at com.zimbra.cs.mailbox.OfflineMailbox.sendRequest(OfflineMailbox.java:736)
	at com.zimbra.cs.mailbox.OfflineMailbox.sendRequest(OfflineMailbox.java:732)
	at com.zimbra.cs.mailbox.OfflineMailbox.sendRequest(OfflineMailbox.java:728)
	at com.zimbra.cs.mailbox.PushChanges.sendRequest(PushChanges.java:628)
	at com.zimbra.cs.mailbox.PushChanges.pushRequest(PushChanges.java:562)
	at com.zimbra.cs.mailbox.PushChanges.syncFolder(PushChanges.java:749)
	at com.zimbra.cs.mailbox.PushChanges.sync(PushChanges.java:309)
	at com.zimbra.cs.mailbox.PushChanges.sync(PushChanges.java:174)
	at com.zimbra.cs.mailbox.MailboxSync.sync(MailboxSync.java:189)
	at com.zimbra.cs.mailbox.OfflineMailbox.sync(OfflineMailbox.java:140)
	at com.zimbra.cs.service.offline.OfflineSync.handle(OfflineSync.java:47)
	at com.zimbra.soap.SoapEngine.dispatchRequest(SoapEngine.java:429)
	at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.java:286)
	at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.java:160)
	at com.zimbra.soap.SoapServlet.doPost(SoapServlet.java:269)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
	at com.zimbra.cs.servlet.ZimbraServlet.service(ZimbraServlet.java:190)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
	at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
	at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362)
	at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
	at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
	at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:716)
	at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:406)
	at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:211)
	at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:139)
	at org.mortbay.jetty.handler.RewriteHandler.handle(RewriteHandler.java:176)
	at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:139)
	at org.mortbay.jetty.Server.handle(Server.java:313)
	at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:506)
	at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:844)
	at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:644)
	at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
	at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:381)
	at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:396)
	at org.mortbay.thread.BoundedThreadPool$PoolThread.run(BoundedThreadPool.java:442)