I am having the same problem here with some users.
My server version is Release 7.1.2_GA_3268.DEBIAN5 DEBIAN5 FOSS edition.
Code:
2011-09-12 14:40:38,950 INFO [btpool0-2://abc.dyndns.org/dav/user%40domain.com/calendar/837a3550-46d8-401f-ab7a-4f4a2980040f.ics] [aname=user@domain.com;ip=xxx.xxx.xxx.xxx;ua=Mozilla/5.0 (Windows NT 6.1;; rv:6.0) Gecko/20110812 Thunderbird/6.0 Lightning/1.0b5;] FileUploadServlet - saveUpload(): received Upload: { accountId=b80fc007-467a-48aa-8f06-52b2f315b046, time=Mon Sep 12 14:40:38 CEST 2011, size=1318, uploadId=49f3b77b-49c4-4a95-92f4-ccb1bc9d2a15:80f1e507-69da-4d28-a295-d25f37772bcf, name=null, path=null }
2011-09-12 14:40:38,953 ERROR [btpool0-2://abc.dyndns.org/dav/user%40domain.com/calendar/837a3550-46d8-401f-ab7a-4f4a2980040f.ics] [aname=user@domain.com;ip=xxx.xxx.xxx.xxx;ua=Mozilla/5.0 (Windows NT 6.1;; rv:6.0) Gecko/20110812 Thunderbird/6.0 Lightning/1.0b5;] dav - error handling method PUT
java.lang.NullPointerException
at com.zimbra.cs.dav.resource.CalendarCollection.createItem(CalendarCollection.java:399)
at com.zimbra.cs.dav.service.method.Put.handle(Put.java:42)
at com.zimbra.cs.dav.service.DavServlet.service(DavServlet.java:226)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:814)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
at com.zimbra.cs.servlet.SetHeaderFilter.doFilter(SetHeaderFilter.java:79)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.servlet.UserAgentFilter.doFilter(UserAgentFilter.java:81)
at org.mortbay.servlet.GzipFilter.doFilter(GzipFilter.java:132)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:218)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:422)
at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.handler.rewrite.RewriteHandler.handle(RewriteHandler.java:230)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.handler.DebugHandler.handle(DebugHandler.java:77)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:543)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:946)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:405)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:410)
at org.mortbay.thread.BoundedThreadPool$PoolThread.run(BoundedThreadPool.java:451)
2011-09-12 14:40:38,954 INFO [btpool0-2://abc.dyndns.org/dav/user%40domain.com/calendar/837a3550-46d8-401f-ab7a-4f4a2980040f.ics] [aname=user@domain.com;ip=xxx.xxx.xxx.xxx;ua=Mozilla/5.0 (Windows NT 6.1;; rv:6.0) Gecko/20110812 Thunderbird/6.0 Lightning/1.0b5;] dav - DavServlet operation PUT to /home/user@domain.com/calendar/837a3550-46d8-401f-ab7a-4f4a2980040f.ics (depth: zero) finished in 4ms