JSF报错：javax.servlet.ServletException

开始用的是GLASSFISH，后来用TOMCAT，信息如下：
exception javax.servlet.ServletException: Error performing conversion of value ' of type class java.lang.String to type class com.numberquiz.ProblemBean for managed bean quiz.
javax.faces.webapp.FacesServlet.service(FacesServlet.java:249)
root cause javax.faces.FacesException: Error performing conversion of value ' of type class java.lang.String to type class com.numberquiz.ProblemBean for managed bean quiz.
com.sun.faces.config.ManagedBeanFactoryImpl.getConvertedValueConsideringPrimitives(ManagedBeanFactoryImpl.java:971)
com.sun.faces.config.ManagedBeanFactoryImpl.setPropertiesIntoBean(ManagedBeanFactoryImpl.java:644)
com.sun.faces.config.ManagedBeanFactoryImpl.newInstance(ManagedBeanFactoryImpl.java:317)
com.sun.faces.application.ApplicationAssociate.createAndMaybeStoreManagedBeans(ApplicationAssociate.java:532)
com.sun.faces.el.ManagedBeanELResolver.getValue(ManagedBeanELResolver.java:82)
javax.el.CompositeELResolver.getValue(CompositeELResolver.java:53)
com.sun.faces.el.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:64)
org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:61)
org.apache.el.parser.AstValue.getValue(AstValue.java:107)
org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:186)
org.apache.jasper.el.JspValueExpression.getValue(JspValueExpression.java:101)
javax.faces.component.UIParameter.getValue(UIParameter.java:156)
com.sun.faces.renderkit.html_basic.OutputMessageRenderer.encodeEnd(OutputMessageRenderer.java:137)
javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:833)
javax.faces.component.UIComponent.encodeAll(UIComponent.java:896)
javax.faces.render.Renderer.encodeChildren(Renderer.java:137)
javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:809)
javax.faces.component.UIComponent.encodeAll(UIComponent.java:886)
javax.faces.component.UIComponent.encodeAll(UIComponent.java:892)
com.sun.faces.application.ViewHandlerImpl.doRenderView(ViewHandlerImpl.java:244)
com.sun.faces.application.ViewHandlerImpl.renderView(ViewHandlerImpl.java:174)
com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:106)
com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:251)
com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:144)
javax.faces.webapp.FacesServlet.service(FacesServlet.java:245)com.numberquiz.ProblemBean 中没有’
com.numberquiz.QuizBean 中也没有’
网上查了，信息很少不知道有谁遇到过的，麻烦说下，谢谢