以下异常的原因可能是什么？我的 persistence.xml 和 components.xml 看起来不错。环境：Tomcat6、Seam2框架。
Oct 17, 2013 10:37:46 AM org.apache.catalina.core.StandardContext listenerStart
SEVERE: Exception sending context initialized event to listener instance of class org.jboss.seam.servlet.SeamListener
org.jboss.seam.InstantiationException: Could not instantiate Seam component: someComponent
at org.jboss.seam.Component.newInstance(Component.java:2170)
at org.jboss.seam.Component.getInstance(Component.java:2024)
at org.jboss.seam.Component.getInstance(Component.java:1986)
at org.jboss.seam.core.Events.raiseEvent(Events.java:77)
at org.jboss.seam.contexts.ServletLifecycle.endInitialization(ServletLifecycle.java:145)
at org.jboss.seam.init.Initialization.init(Initialization.java:744)
at org.jboss.seam.servlet.SeamListener.contextInitialized(SeamListener.java:36)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3843)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4342)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
at org.apache.catalina.core.StandardHost.start(StandardHost.java:719)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
at org.apache.catalina.core.StandardService.start(StandardService.java:516)
at org.apache.catalina.core.StandardServer.start(StandardServer.java:710)
at org.apache.catalina.startup.Catalina.start(Catalina.java:578)
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.catalina.startup.Bootstrap.start(Bootstrap.java:288)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:413)
Caused by: java.lang.RuntimeException: exception invoking: getTransaction
at org.jboss.seam.util.Reflections.invokeAndWrap(Reflections.java:154)
at org.jboss.seam.Component.callComponentMethod(Component.java:2275)
at org.jboss.seam.Component.unwrap(Component.java:2301)
at org.jboss.seam.Component.getInstance(Component.java:2044)
at org.jboss.seam.Component.getInstance(Component.java:2003)
at org.jboss.seam.Component.getInstance(Component.java:1997)
at org.jboss.seam.Component.getInstance(Component.java:1970)
at org.jboss.seam.Component.getInstance(Component.java:1965)
at org.jboss.seam.transaction.Transaction.instance(Transaction.java:39)
at org.jboss.seam.persistence.ManagedPersistenceContext.joinTransaction(ManagedPersistenceContext.java:120)
at org.jboss.seam.persistence.ManagedPersistenceContext.getEntityManager(ManagedPersistenceContext.java:112)
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.jboss.seam.util.Reflections.invoke(Reflections.java:22)
at org.jboss.seam.util.Reflections.invokeAndWrap(Reflections.java:144)
at org.jboss.seam.Component.callComponentMethod(Component.java:2275)
at org.jboss.seam.Component.unwrap(Component.java:2301)
at org.jboss.seam.Component.getInstance(Component.java:2044)
at org.jboss.seam.Component.getInstance(Component.java:1986)
at org.jboss.seam.Component.getInstance(Component.java:1980)
at org.jboss.seam.Component.getInstanceInAllNamespaces(Component.java:2375)
at org.jboss.seam.Component.getValueToInject(Component.java:2327)
at org.jboss.seam.Component.injectAttributes(Component.java:1739)
at org.jboss.seam.Component.inject(Component.java:1557)
at org.jboss.seam.core.BijectionInterceptor.aroundInvoke(BijectionInterceptor.java:61)
at org.jboss.seam.intercept.SeamInvocationContext.proceed(SeamInvocationContext.java:68)
at org.jboss.seam.core.MethodContextInterceptor.aroundInvoke(MethodContextInterceptor.java:44)
at org.jboss.seam.intercept.SeamInvocationContext.proceed(SeamInvocationContext.java:68)
at org.jboss.seam.intercept.RootInterceptor.invoke(RootInterceptor.java:107)
at org.jboss.seam.intercept.JavaBeanInterceptor.interceptInvocation(JavaBeanInterceptor.java:185)
at org.jboss.seam.intercept.JavaBeanInterceptor.invoke(JavaBeanInterceptor.java:103)
at pg.exess.manager.ExessBusinessUnitManager_$$_javassist_seam_2.create(ExessBusinessUnitManager_$$_javassist_seam_2.java)
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.jboss.seam.util.Reflections.invoke(Reflections.java:22)
at org.jboss.seam.util.Reflections.invokeAndWrap(Reflections.java:144)
at org.jboss.seam.Component.callComponentMethod(Component.java:2275)
at org.jboss.seam.Component.callCreateMethod(Component.java:2198)
at org.jboss.seam.Component.newInstance(Component.java:2158)
... 21 more
Caused by: javax.naming.NamingException: Cannot create resource instance
at org.apache.naming.factory.TransactionFactory.getObjectInstance(TransactionFactory.java:113)
at javax.naming.spi.NamingManager.getObjectInstance(NamingManager.java:304)
at org.apache.naming.NamingContext.lookup(NamingContext.java:793)
at org.apache.naming.NamingContext.lookup(NamingContext.java:140)
at org.apache.naming.NamingContext.lookup(NamingContext.java:781)
at org.apache.naming.NamingContext.lookup(NamingContext.java:153)
at org.apache.naming.SelectorContext.lookup(SelectorContext.java:137)
at javax.naming.InitialContext.lookup(InitialContext.java:392)
at org.jboss.seam.transaction.Transaction.getUserTransaction(Transaction.java:82)
at org.jboss.seam.transaction.Transaction.createUTTransaction(Transaction.java:74)
at org.jboss.seam.transaction.Transaction.getTransaction(Transaction.java:47)
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.jboss.seam.util.Reflections.invoke(Reflections.java:22)
at org.jboss.seam.util.Reflections.invokeAndWrap(Reflections.java:144)
... 63 more
Oct 17, 2013 10:37:46 AM org.apache.catalina.core.StandardContext start
SEVERE: Error listenerStart
Oct 17, 2013 10:37:46 AM org.apache.catalina.core.StandardContext start
SEVERE: Context [/project] startup failed due to previous errors
谢谢你的帮助！