normal page throws exception after installed zkspring

a simple zul throws exception when working with zkspring.
step, just click the button.
==zul
<zk>
<button label="zkspring!!" >
</button>
</zk>
==
SEVERE: >>org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'event': Invocation of init method failed; nested exception is org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'event': Requested bean is currently in creation: Is there an unresolvable circular reference?
>>org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'event': Requested bean is currently in creation: Is there an unresolvable circular reference?
>> at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:224)
>> at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
>> at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
>> at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:881)
>> at org.zkoss.spring.DelegatingVariableResolver.resolveVariable(DelegatingVariableResolver.java:75)
>>...