Content editors are unable to activate content changes. The sequence is:
1. Edit existing page.
2. Click activate.
3. Activation failure is not reported in the UI but no email is sent to the next user in the approval workflow and the following stack trace appears in the server log:

2010-02-09 10:29:38,253 INFO [STDOUT] ERROR info.magnolia.module.workflow.WorkflowUtil WorkflowUtil.java(launchFlow:80) 09.02.2010 10:29:38 Launching flow failed
openwfe.org.engine.launch.LaunchException: launch failed
at openwfe.org.engine.impl.launch.SimpleXmlLauncher.launch(SimpleXmlLauncher.java:326)
at openwfe.org.engine.impl.launch.SimpleXmlLauncher.launch(SimpleXmlLauncher.java:122)
at openwfe.org.embed.impl.engine.AbstractEngine.launch(AbstractEngine.java:214)
at info.magnolia.module.workflow.WorkflowUtil.launchFlow(WorkflowUtil.java:77)
at info.magnolia.module.workflow.WorkflowUtil.launchFlow(WorkflowUtil.java:118)
at info.magnolia.module.workflow.commands.FlowCommand.execute(FlowCommand.java:57)
at info.magnolia.commands.MgnlCommand.executePooledOrSynchronized(MgnlCommand.java:141)
at info.magnolia.commands.MgnlCommand.execute(MgnlCommand.java:128)
at org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
at info.magnolia.cms.servlets.CommandBasedMVCServletHandler.execute(CommandBasedMVCServletHandler.java:78)
at info.magnolia.cms.servlets.MVCServlet.doPost(MVCServlet.java:111)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at info.magnolia.cms.filters.MagnoliaManagedFilter$CustomFilterChain.doFilter(MagnoliaManagedFilter.java:88)
at info.magnolia.cms.filters.MgnlCmsFilter.doFilter(MgnlCmsFilter.java:103)
at info.magnolia.cms.filters.MagnoliaManagedFilter$CustomFilterChain.doFilter(MagnoliaManagedFilter.java:92)
at info.magnolia.cms.cache.CacheFilter.doFilter(CacheFilter.java:96)
at info.magnolia.cms.filters.MagnoliaManagedFilter$CustomFilterChain.doFilter(MagnoliaManagedFilter.java:92)
at info.magnolia.cms.filters.MgnlInterceptFilter.doFilter(MgnlInterceptFilter.java:132)
at info.magnolia.cms.filters.MagnoliaManagedFilter$CustomFilterChain.doFilter(MagnoliaManagedFilter.java:92)
at info.magnolia.cms.filters.MgnlContextFilter.doFilter(MgnlContextFilter.java:45)
at info.magnolia.cms.filters.MagnoliaManagedFilter$CustomFilterChain.doFilter(MagnoliaManagedFilter.java:92)
at info.magnolia.cms.security.SecurityFilter.doFilter(SecurityFilter.java:100)
at info.magnolia.cms.filters.MagnoliaManagedFilter$CustomFilterChain.doFilter(MagnoliaManagedFilter.java:92)
at info.magnolia.cms.filters.MultipartRequestFilter.doFilter(MultipartRequestFilter.java:80)
at info.magnolia.cms.filters.MagnoliaManagedFilter$CustomFilterChain.doFilter(MagnoliaManagedFilter.java:92)
at info.magnolia.cms.filters.MgnlVirtualUriFilter.doFilter(MgnlVirtualUriFilter.java:83)
at info.magnolia.cms.filters.MagnoliaManagedFilter$CustomFilterChain.doFilter(MagnoliaManagedFilter.java:92)
at info.magnolia.cms.filters.ContentTypeFilter.doFilter(ContentTypeFilter.java:66)
at info.magnolia.cms.filters.MagnoliaManagedFilter$CustomFilterChain.doFilter(MagnoliaManagedFilter.java:92)
at info.magnolia.enterprise.registration.RegistrationFilter.doFilter(RegistrationFilter.java:77)
at info.magnolia.cms.filters.MagnoliaManagedFilter$CustomFilterChain.doFilter(MagnoliaManagedFilter.java:92)
at info.magnolia.cms.filters.MagnoliaManagedFilter.doFilter(MagnoliaManagedFilter.java:65)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:175)
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:74)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.jboss.web.tomcat.tc5.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:156)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:199)
at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:282)
at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:767)
at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:697)
at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:889)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Unknown Source)
Caused by: openwfe.org.engine.expool.PoolException: storeExpression() store exception failed
at info.magnolia.module.workflow.jcr.JCRExpressionStore.storeExpression(JCRExpressionStore.java:122)
at openwfe.org.engine.impl.expool.SimpleExpressionPool.add(SimpleExpressionPool.java:349)
at openwfe.org.engine.impl.expool.CachedExpressionPool.add(CachedExpressionPool.java:155)
at openwfe.org.engine.impl.launch.SimpleXmlLauncher.launch(SimpleXmlLauncher.java:300)
... 55 more
Caused by: javax.jcr.InvalidItemStateException: 97c54973-b32c-4252-bef6-fff374eb3879: the item cannot be saved because it has been modified externally.
at org.apache.jackrabbit.core.ItemImpl.getTransientStates(ItemImpl.java:387)
at org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:1054)
at org.apache.jackrabbit.core.SessionImpl.save(SessionImpl.java:805)
at info.magnolia.cms.core.HierarchyManager.save(HierarchyManager.java:525)
at info.magnolia.module.workflow.jcr.JCRExpressionStore.storeExpression(JCRExpressionStore.java:114)
... 58 more

As indicated in the priority field this is a blocker for updates to our production site.