Internal server error when contents are posted at the same time

[java] java.util.ConcurrentModificationException
[java] at com.hp.hpl.jena.tdb.store.GraphTDBBase$MapperIteratorTriples.checkCourrentModification(GraphTDBBase.java:208)
[java] at com.hp.hpl.jena.tdb.store.GraphTDBBase$MapperIteratorTriples.hasNext(GraphTDBBase.java:216)
[java] at org.apache.clerezza.rdf.jena.storage.JenaGraphAdaptor$1.hasNext(JenaGraphAdaptor.java:106)
[java] at org.apache.clerezza.rdf.core.impl.AbstractTripleCollection$1.hasNext(AbstractTripleCollection.java:78)
[java] at org.apache.clerezza.rdf.core.access.LockingIterator.hasNext(LockingIterator.java:47)
[java] at org.apache.stanbol.contenthub.store.solr.SolrStoreImpl.removeEnhancements(SolrStoreImpl.java:260)
[java] at org.apache.stanbol.contenthub.store.solr.SolrStoreImpl.updateEnhancementGraph(SolrStoreImpl.java:273)
[java] at org.apache.stanbol.contenthub.store.solr.SolrStoreImpl.put(SolrStoreImpl.java:318)
[java] at org.apache.stanbol.contenthub.store.solr.SolrStoreImpl.enhanceAndPut(SolrStoreImpl.java:288)
[java] at org.apache.stanbol.contenthub.web.resources.StoreResource.createEnhanceAndRedirect(StoreResource.java:606)
[java] at org.apache.stanbol.contenthub.web.resources.StoreResource.createContentItemWithRawData(StoreResource.java:498)
[java] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[java] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
[java] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[java] at java.lang.reflect.Method.invoke(Method.java:601)
[java] at com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60)
[java] at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$ResponseOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:205)
[java] at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75)
[java] at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:302)
[java] at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:108)
[java] at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
[java] at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84)
[java] at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1480)
[java] at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1411)
[java] at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1360)
[java] at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1350)
[java] at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)
[java] at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:538)
[java] at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:716)
[java] at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
[java] at org.apache.felix.http.base.internal.handler.ServletHandler.doHandle(ServletHandler.java:96)
[java] at org.apache.felix.http.base.internal.handler.ServletHandler.handle(ServletHandler.java:79)
[java] at org.apache.felix.http.base.internal.dispatch.ServletPipeline.handle(ServletPipeline.java:42)
[java] at org.apache.felix.http.base.internal.dispatch.InvocationFilterChain.doFilter(InvocationFilterChain.java:49)
[java] at org.apache.felix.http.base.internal.dispatch.HttpFilterChain.doFilter(HttpFilterChain.java:33)
[java] at org.apache.stanbol.commons.httpqueryheaders.impl.QueryHeadersFilter.doFilter(QueryHeadersFilter.java:75)
[java] at org.apache.felix.http.base.internal.handler.FilterHandler.doHandle(FilterHandler.java:88)
[java] at org.apache.felix.http.base.internal.handler.FilterHandler.handle(FilterHandler.java:76)
[java] at org.apache.felix.http.base.internal.dispatch.InvocationFilterChain.doFilter(InvocationFilterChain.java:47)
[java] at org.apache.felix.http.base.internal.dispatch.HttpFilterChain.doFilter(HttpFilterChain.java:33)
[java] at org.apache.felix.http.base.internal.handler.FilterHandler.handle(FilterHandler.java:78)
[java] at org.apache.felix.http.base.internal.dispatch.InvocationFilterChain.doFilter(InvocationFilterChain.java:47)
[java] at org.apache.felix.http.base.internal.dispatch.HttpFilterChain.doFilter(HttpFilterChain.java:33)
[java] at org.apache.stanbol.commons.web.resources.ResourceServingFilter.doFilterHttp(ResourceServingFilter.java:148)
[java] at org.apache.stanbol.commons.web.resources.ResourceServingFilter.doFilter(ResourceServingFilter.java:91)
[java] at org.apache.felix.http.base.internal.handler.FilterHandler.doHandle(FilterHandler.java:88)
[java] at org.apache.felix.http.base.internal.handler.FilterHandler.handle(FilterHandler.java:76)
[java] at org.apache.felix.http.base.internal.dispatch.InvocationFilterChain.doFilter(InvocationFilterChain.java:47)
[java] at org.apache.felix.http.base.internal.dispatch.HttpFilterChain.doFilter(HttpFilterChain.java:33)
[java] at org.apache.stanbol.commons.security.auth.AuthenticatingFilter$1.run(AuthenticatingFilter.java:163)
[java] at java.security.AccessController.doPrivileged(Native Method)
[java] at javax.security.auth.Subject.doAsPrivileged(Subject.java:536)
[java] at org.apache.stanbol.commons.security.auth.AuthenticatingFilter.doFilter(AuthenticatingFilter.java:159)
[java] at org.apache.felix.http.base.internal.handler.FilterHandler.doHandle(FilterHandler.java:88)
[java] at org.apache.felix.http.base.internal.handler.FilterHandler.handle(FilterHandler.java:76)
[java] at org.apache.felix.http.base.internal.dispatch.InvocationFilterChain.doFilter(InvocationFilterChain.java:47)
[java] at org.apache.felix.http.base.internal.dispatch.HttpFilterChain.doFilter(HttpFilterChain.java:33)
[java] at org.apache.felix.http.base.internal.dispatch.FilterPipeline.dispatch(FilterPipeline.java:48)
[java] at org.apache.felix.http.base.internal.dispatch.Dispatcher.dispatch(Dispatcher.java:39)
[java] at org.apache.felix.http.base.internal.DispatcherServlet.service(DispatcherServlet.java:67)
[java] at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
[java] at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
[java] at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:390)
[java] at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
[java] at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
[java] at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
[java] at org.mortbay.jetty.Server.handle(Server.java:326)
[java] at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
[java] at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:943)
[java] at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)
[java] at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
[java] at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
[java] at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:410)
[java] at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)