Create namespace fails with ClassCastException

• log in to CMS
• go to browse tab
• go to configuration
• select 'create namespace' from dropdown
• fill in 'test' in prefix, and 'http://example.org/test' in UR:
• click OK
• java.lang.ClassCastException: $Proxy9

Full stacktrace:

06.10.2008 11:58:42 ERROR [org.hippoecm.frontend.dialog.AbstractDialog$2.onClick():80] java.lang.ClassCastException: $Proxy9
java.lang.ClassCastException: $Proxy9
at org.hippoecm.frontend.plugins.standardworkflow.dialogs.NamespaceDialog.execute(NamespaceDialog.java:50)
at org.hippoecm.frontend.dialog.AbstractWorkflowDialog.ok(AbstractWorkflowDialog.java:112)
at org.hippoecm.frontend.dialog.AbstractDialog$2.onClick(AbstractDialog.java:76)
at org.apache.wicket.ajax.markup.html.AjaxLink$1.onEvent(AjaxLink.java:65)
at org.apache.wicket.ajax.AjaxEventBehavior.respond(AjaxEventBehavior.java:163)
at org.apache.wicket.ajax.AbstractDefaultAjaxBehavior.onRequest(AbstractDefaultAjaxBehavior.java:293)
at org.apache.wicket.request.target.component.listener.BehaviorRequestTarget.processEvents(BehaviorRequestTarget.java:100)
at org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:91)
at org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1171)
at org.apache.wicket.RequestCycle.step(RequestCycle.java:1248)
at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1349)
at org.apache.wicket.RequestCycle.request(RequestCycle.java:493)
at org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:387)
at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:199)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:360)
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:726)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:206)
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:505)
at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:829)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:514)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)