I am trying to setup an outbound interceptor for my webservice security header. However, when I instantiate WSS4JStaxOutInterceptor class like following:

Map<String, Object> outboundProp = new HashMap<String, Object>();

//Inserting some outbound properties

WSS4JStaxOutInterceptor outInterceptor = new WSS4JStaxOutInterceptor(outboundProp);

I get following exception

Caused by: java.lang.RuntimeException: 
org.apache.xml.security.stax.impl.resourceResolvers.ResolverFilesystem 
cannot be cast to org.apache.xml.security.stax.ext.ResourceResolverLookup
        at org.apache.wss4j.stax.setup.WSSec.<clinit>(WSSec.java:84)
        ... 16 more

Caused by: org.apache.xml.security.stax.ext.XMLSecurityConfigurationException: 
org.apache.xml.security.stax.impl.resourceResolvers.ResolverFilesystem 
cannot be cast to org.apache.xml.security.stax.ext.ResourceResolverLookup
Original Exception was java.lang.ClassCastException: 
org.apache.xml.security.stax.impl.resourceResolvers.ResolverFilesystem 
cannot be cast to org.apache.xml.security.stax.ext.ResourceResolverLookup
        at org.apache.xml.security.stax.config.Init.init(Init.java:92)
        at org.apache.wss4j.stax.setup.WSSec.<clinit>(WSSec.java:62)
        ... 16 more

Caused by: java.lang.ClassCastException: 
org.apache.xml.security.stax.impl.resourceResolvers.ResolverFilesystem 
cannot be cast to org.apache.xml.security.stax.ext.ResourceResolverLookup
        at org.apache.xml.security.stax.config.ResourceResolverMapper.init(ResourceResolverMapper.java:48)
        at org.apache.xml.security.stax.config.Init.init(Init.java:85)
        ... 17 more

What is really weird is ResolverFilesystem implements ResourceResolverLookup. So why would it throw class cast exception?

Your help is greatly appreciated.