Workflow is no longer possible after event logging failed with an InvalidItemStateException

When logging in, an InvalidItemStateException is sometimes shown in the (server) logs. Hereafter, no workflow steps are possible.
I've attached two stacktraces; one the original error, the other is one of the stacks that arise when invoking a workflow after this occurred.

Stacktrace from the login:

06.02.2009 14:46:59 WARN [org.hippoecm.repository.standardworkflow.EventLoggerImpl.logWorkflowStep():102] Event logging failed: 0e6d718f-b8ca-4556-b264-885a85337db4 has been modified externally
javax.jcr.InvalidItemStateException: 0e6d718f-b8ca-4556-b264-885a85337db4 has been modified externally
at org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:1109)
at org.hippoecm.repository.decorating.ItemDecorator.save(ItemDecorator.java:144)
at org.hippoecm.repository.impl.NodeDecorator.save(NodeDecorator.java:79)
at org.hippoecm.repository.standardworkflow.EventLoggerImpl.logWorkflowStep(EventLoggerImpl.java:99)
at org.hippoecm.repository.impl.WorkflowManagerImpl$WorkflowInvocationHandler.invoke(WorkflowManagerImpl.java:472)
at $Proxy2.list(Unknown Source)
at org.hippoecm.frontend.plugins.standardworkflow.AbstractFolderWorkflowPlugin.onModelChanged(AbstractFolderWorkflowPlugin.java:146)
at org.apache.wicket.Component.modelChanged(Component.java:2105)
at org.hippoecm.frontend.plugin.workflow.AbstractWorkflowPlugin.start(AbstractWorkflowPlugin.java:84)
at org.hippoecm.frontend.plugin.impl.PluginContext.connect(PluginContext.java:182)
at org.hippoecm.frontend.plugin.impl.PluginManager.start(PluginManager.java:84)
at org.hippoecm.frontend.plugin.impl.PluginContext.start(PluginContext.java:198)
at org.hippoecm.frontend.plugin.impl.ClusterControl.start(ClusterControl.java:110)
at org.hippoecm.frontend.plugin.workflow.WorkflowPlugin$Cluster.<init>(WorkflowPlugin.java:66)
at org.hippoecm.frontend.plugin.workflow.WorkflowPlugin.showWorkflow(WorkflowPlugin.java:198)
at org.hippoecm.frontend.plugin.workflow.WorkflowPlugin.updateModel(WorkflowPlugin.java:167)
at org.hippoecm.frontend.plugin.workflow.WorkflowPlugin.<init>(WorkflowPlugin.java:107)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at org.hippoecm.frontend.plugin.impl.PluginFactory.createPlugin(PluginFactory.java:70)
at org.hippoecm.frontend.plugin.impl.PluginManager.start(PluginManager.java:82)
at org.hippoecm.frontend.plugin.impl.PluginContext.start(PluginContext.java:198)
at org.hippoecm.frontend.plugin.impl.ClusterControl.start(ClusterControl.java:110)
at org.hippoecm.frontend.Home.<init>(Home.java:91)
at org.hippoecm.frontend.plugins.login.LoginPlugin$SignInForm.onSubmit(LoginPlugin.java:199)
at org.apache.wicket.markup.html.form.Form.delegateSubmit(Form.java:1355)
at org.apache.wicket.markup.html.form.Form.onFormSubmitted(Form.java:810)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.wicket.RequestListenerInterface.invoke(RequestListenerInterface.java:183)
at org.apache.wicket.request.target.component.listener.ListenerInterfaceRequestTarget.processEvents(ListenerInterfaceRequestTarget.java:73)

From the workflow that is invoked later:

06.02.2009 14:51:15 ERROR [org.hippoecm.frontend.plugin.workflow.AbstractWorkflowPlugin.execute():233] Invalid data to save
javax.jcr.nodetype.ConstraintViolationException: 0b611f2b-5913-4fea-9010-e5d5f1891797 needs to be saved as well.
at org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:1049)
at org.apache.jackrabbit.core.SessionImpl.save(SessionImpl.java:846)
at org.hippoecm.repository.decorating.SessionDecorator.save(SessionDecorator.java:202)
at org.hippoecm.repository.impl.SessionDecorator.save(SessionDecorator.java:145)
at org.hippoecm.repository.impl.WorkflowManagerImpl$WorkflowInvocationHandler.invoke(WorkflowManagerImpl.java:466)
at $Proxy3.commitEditableInstance(Unknown Source)
at org.hippoecm.frontend.plugins.reviewedactions.EditingReviewedActionsWorkflowPlugin$1.execute(EditingReviewedActionsWorkflowPlugin.java:67)
at org.hippoecm.frontend.plugin.workflow.AbstractWorkflowPlugin.execute(AbstractWorkflowPlugin.java:229)
at org.hippoecm.frontend.plugin.workflow.AbstractWorkflowPlugin.access$0(AbstractWorkflowPlugin.java:206)
at org.hippoecm.frontend.plugin.workflow.AbstractWorkflowPlugin$2.onClick(AbstractWorkflowPlugin.java:150)
at org.apache.wicket.ajax.markup.html.AjaxLink$1.onEvent(AjaxLink.java:65)
at org.apache.wicket.ajax.AjaxEventBehavior.respond(AjaxEventBehavior.java:163)
at org.apache.wicket.ajax.AbstractDefaultAjaxBehavior.onRequest(AbstractDefaultAjaxBehavior.java:297)
at org.apache.wicket.request.target.component.listener.BehaviorRequestTarget.processEvents(BehaviorRequestTarget.java:100)
at org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:91)