InvalidItemStateException; item cannot be saved because it has beenmodified externally: Node /

Occurred twice, in near proximity (~2 minutes):
14.07.2010 11:05:00 ERROR [org.hippoecm.addon.workflow.CompatibilityWorkflowPlugin$WorkflowAction.invoke():139] Workflow call failed
javax.jcr.InvalidItemStateException: Item cannot be saved because it has beenmodified externally: node /
at org.apache.jackrabbit.core.ItemImpl.getTransientStates(ItemImpl.java:246)
at org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:929)
at org.apache.jackrabbit.core.SessionImpl.save(SessionImpl.java:858)
at org.hippoecm.repository.decorating.SessionDecorator.save(SessionDecorator.java:202)
at org.hippoecm.repository.impl.SessionDecorator.save(SessionDecorator.java:179)
at org.hippoecm.repository.decorating.checked.SessionDecorator.save(SessionDecorator.java:227)
at org.hippoecm.addon.workflow.CompatibilityWorkflowPlugin$WorkflowAction.execute(CompatibilityWorkflowPlugin.java:157)
at org.hippoecm.addon.workflow.CompatibilityWorkflowPlugin$WorkflowAction.execute(CompatibilityWorkflowPlugin.java:146)
at org.hippoecm.addon.workflow.CompatibilityWorkflowPlugin$WorkflowAction.invoke(CompatibilityWorkflowPlugin.java:134)
at org.hippoecm.addon.workflow.StdWorkflow$1$1.onClick(StdWorkflow.java:59)
at org.hippoecm.addon.workflow.MenuLink.onClick(MenuLink.java:50)
at org.apache.wicket.ajax.markup.html.AjaxLink$1.onEvent(AjaxLink.java:68)
at org.apache.wicket.ajax.AjaxEventBehavior.respond(AjaxEventBehavior.java:177)
at org.apache.wicket.ajax.AbstractDefaultAjaxBehavior.onRequest(AbstractDefaultAjaxBehavior.java:286)
at org.apache.wicket.request.target.component.listener.BehaviorRequestTarget.processEvents(BehaviorRequestTarget.java:119)
at org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:92)
at org.hippoecm.frontend.PluginRequestCycleProcessor.processEvents(PluginRequestCycleProcessor.java:95)
at org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1250)
at org.apache.wicket.RequestCycle.step(RequestCycle.java:1329)
at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1428)
at org.apache.wicket.RequestCycle.request(RequestCycle.java:545)
at org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:479)
at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:312)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1115)
at org.hippoecm.frontend.plugins.login.ConcurrentLoginFilter.doFilter(ConcurrentLoginFilter.java:54)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1115)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:361)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:766)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:417)
at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:324)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:534)
at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:864)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:533)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:207)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:403)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:522)