How to repeat:  In a group config, click the "View Group Update" link of any history item.  Then try to open the modal dialog for values that differ.  You get the following exception:

com.sun.facelets.tag.TagAttributeException: /rhq/group/layout/main.xhtml @33,137 template="${(ResourceGroupUIBean.compatible) ? '/rhq/entity/layout/main.xhtml' : '/rhq/entity/layout/main-wide.xhtml'}" Cant instantiate class: org.rhq.enterprise.gui.inventory.group.ResourceGroupUIBean.
	at com.sun.facelets.tag.TagAttribute.getObject(TagAttribute.java:235)
	at com.sun.facelets.tag.TagAttribute.getValue(TagAttribute.java:200)
	at com.sun.facelets.tag.ui.CompositionHandler.apply(CompositionHandler.java:113)
	at com.sun.facelets.compiler.NamespaceHandler.apply(NamespaceHandler.java:49)
	at com.sun.facelets.compiler.EncodingHandler.apply(EncodingHandler.java:25)
	at com.sun.facelets.impl.DefaultFacelet.include(DefaultFacelet.java:248)
	at com.sun.facelets.impl.DefaultFacelet.include(DefaultFacelet.java:294)
	at com.sun.facelets.impl.DefaultFacelet.include(DefaultFacelet.java:273)
	at com.sun.facelets.impl.DefaultFaceletContext.includeFacelet(DefaultFaceletContext.java:144)
	at com.sun.facelets.tag.ui.CompositionHandler.apply(CompositionHandler.java:113)
	at com.sun.facelets.compiler.NamespaceHandler.apply(NamespaceHandler.java:49)
	at com.sun.facelets.compiler.EncodingHandler.apply(EncodingHandler.java:25)
	at com.sun.facelets.impl.DefaultFacelet.apply(DefaultFacelet.java:95)
	at com.sun.facelets.FaceletViewHandler.buildView(FaceletViewHandler.java:524)
	at com.sun.facelets.FaceletViewHandler.renderView(FaceletViewHandler.java:567)
	at org.ajax4jsf.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:100)
	at org.ajax4jsf.application.AjaxViewHandler.renderView(AjaxViewHandler.java:176)
	at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:110)
	at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:100)
	at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
	at javax.faces.webapp.FacesServlet.service(FacesServlet.java:266)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.ajax4jsf.webapp.BaseFilter.doFilter(BaseFilter.java:532)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.rhq.enterprise.gui.legacy.WebUserTrackingFilter.doFilter(WebUserTrackingFilter.java:47)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.rhq.enterprise.gui.legacy.AuthenticationFilter.doFilter(AuthenticationFilter.java:129)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:83)
	at org.jboss.seam.web.IdentityFilter.doFilter(IdentityFilter.java:38)
	at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
	at org.jboss.seam.web.MultipartFilter.doFilter(MultipartFilter.java:90)
	at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
	at org.jboss.seam.web.ExceptionFilter.doFilter(ExceptionFilter.java:64)
	at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
	at org.jboss.seam.web.RedirectFilter.doFilter(RedirectFilter.java:45)
	at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
	at org.ajax4jsf.webapp.BaseXMLFilter.doXmlFilter(BaseXMLFilter.java:178)
	at org.ajax4jsf.webapp.BaseFilter.handleRequest(BaseFilter.java:290)
	at org.ajax4jsf.webapp.BaseFilter.processUploadsAndHandleRequest(BaseFilter.java:390)
	at org.ajax4jsf.webapp.BaseFilter.doFilter(BaseFilter.java:517)
	at org.jboss.seam.web.Ajax4jsfFilter.doFilter(Ajax4jsfFilter.java:56)
	at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
	at org.jboss.seam.web.LoggingFilter.doFilter(LoggingFilter.java:58)
	at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:69)
	at org.jboss.seam.servlet.SeamFilter.doFilter(SeamFilter.java:158)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.rhq.helpers.rtfilter.filter.RtFilter.doFilter(RtFilter.java:123)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
	at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:179)
	at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
	at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:241)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:580)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
	at java.lang.Thread.run(Thread.java:619)
Caused by: com.sun.faces.mgbean.ManagedBeanCreationException: Cant instantiate class: org.rhq.enterprise.gui.inventory.group.ResourceGroupUIBean.
	at com.sun.faces.mgbean.BeanBuilder.newBeanInstance(BeanBuilder.java:191)
	at com.sun.faces.mgbean.BeanBuilder.build(BeanBuilder.java:106)
	at com.sun.faces.mgbean.BeanManager.createAndPush(BeanManager.java:368)
	at com.sun.faces.mgbean.BeanManager.create(BeanManager.java:230)
	at com.sun.faces.el.ManagedBeanELResolver.getValue(ManagedBeanELResolver.java:86)
	at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:53)
	at com.sun.faces.el.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:72)
	at org.jboss.el.parser.AstIdentifier.getValue(AstIdentifier.java:44)
	at org.jboss.el.parser.AstValue.getValue(AstValue.java:63)
	at org.jboss.el.parser.AstChoice.getValue(AstChoice.java:27)
	at org.jboss.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:186)
	at com.sun.facelets.el.TagValueExpression.getValue(TagValueExpression.java:71)
	at com.sun.facelets.tag.TagAttribute.getObject(TagAttribute.java:233)
	... 70 more
Caused by: java.lang.IllegalStateException: Required request parameter 'groupId' is missing.
	at org.rhq.core.gui.util.FacesContextUtility.getRequiredRequestParameter(FacesContextUtility.java:101)
	at org.rhq.enterprise.gui.inventory.group.ResourceGroupUIBean.lookupResourceGroup(ResourceGroupUIBean.java:212)
	at org.rhq.enterprise.gui.inventory.group.ResourceGroupUIBean.<init>(ResourceGroupUIBean.java:62)
	at sun.reflect.GeneratedConstructorAccessor429.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
	at java.lang.Class.newInstance0(Class.java:355)
	at java.lang.Class.newInstance(Class.java:308)
	at com.sun.faces.mgbean.BeanBuilder.newBeanInstance(BeanBuilder.java:186)
	... 82 more