The issue:

• An index page uses Composition (org.zkoss.zk.ui.util.Composition) and defines content to fill a common template for page layout (<?init class="org.zkoss.zk.ui.util.Composition" arg0="~./template/public-page-template.zul"?>)
• A Div element with ID "headerDiv" is defined in page template (<div id="header" style="background-color:grey; width: 100%; height: 100px" />)
• A custom error page (error.zul, defined in web.xml <error-page> elements) uses the same common page template to show an error message when exception occurs while loading ZUML document.
• When Exception is thrown while composing an index page, composing the error page fails with the following exception:

SEVERE: Exception Processing ErrorPage[exceptionType=java.lang.Throwable, location=/error.zul]
org.zkoss.zk.ui.UiException: Replicated UUID is not allowed for class org.zkoss.zhtml.Div: header
at org.zkoss.zk.ui.AbstractComponent.setId(AbstractComponent.java:513)
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.zkoss.zk.ui.metainfo.Property.assign0(Property.java:284)
at org.zkoss.zk.ui.metainfo.Property.assign(Property.java:169)
at org.zkoss.zk.ui.metainfo.ComponentInfo.applyProperties(ComponentInfo.java:729)
at org.zkoss.zk.ui.impl.AbstractUiFactory.newComponent(AbstractUiFactory.java:106)
at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild0(UiEngineImpl.java:809)
at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild(UiEngineImpl.java:778)
at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate0(UiEngineImpl.java:687)
at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate(UiEngineImpl.java:651)
at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild0(UiEngineImpl.java:824)
at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild(UiEngineImpl.java:778)
at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate0(UiEngineImpl.java:687)
at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate(UiEngineImpl.java:651)
at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild0(UiEngineImpl.java:824)
at org.zkoss.zk.ui.impl.UiEngineImpl.execCreateChild(UiEngineImpl.java:778)
at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate0(UiEngineImpl.java:687)
at org.zkoss.zk.ui.impl.UiEngineImpl.execCreate(UiEngineImpl.java:651)
at org.zkoss.zk.ui.impl.UiEngineImpl.createComponents(UiEngineImpl.java:1032)
at org.zkoss.zk.ui.impl.AbstractExecution.createComponents0(AbstractExecution.java:246)
at org.zkoss.zk.ui.impl.AbstractExecution.createComponents(AbstractExecution.java:238)
at org.zkoss.zk.ui.util.Composition.doInit(Composition.java:92)
at org.zkoss.zk.ui.metainfo.InitiatorInfo.doInit(InitiatorInfo.java:148)
at org.zkoss.zk.ui.metainfo.InitiatorInfo.newInitiator(InitiatorInfo.java:143)
at org.zkoss.zk.ui.metainfo.PageDefinition.doInit(PageDefinition.java:396)
at org.zkoss.zk.ui.impl.Initiators.doInit(Initiators.java:58)
at org.zkoss.zk.ui.impl.UiEngineImpl.execNewPage0(UiEngineImpl.java:382)
at org.zkoss.zk.ui.impl.UiEngineImpl.execNewPage(UiEngineImpl.java:316)
at org.zkoss.zk.ui.http.DHtmlLayoutServlet.process(DHtmlLayoutServlet.java:215)
at org.zkoss.zk.ui.http.DHtmlLayoutServlet.doGet(DHtmlLayoutServlet.java:136)
...

See attached sample project to reproduce the issue:
GET http://localhost:9090/webapp/404 Will result in 404 error and compose the error page correctly
GET http://localhost:9090/webapp/index.zul Will result in the reported exception (Replicated UUID is not allowed)