OpenSAML user discussion

Hi.

I'm using the SAML profile of XACML to set a response into a policy 
evaluation but I'm having problems when building the StatusMessageType. This 
is an interface with no implementation, but it extends the XSString schema, 
so I thought I could first build a XSString object and then cast it to a 
StatusMessageType to set it on the StatusType object, but it raises a 
CastException:

java.lang.ClassCastException: org.opensaml.xml.schema.impl.XSStringImpl 
cannot be cast to org.opensaml.xacml.ctx.StatusMessageType

Can anyone write some lines about how to build an StatusMessageType, set its 
value and put it into a StatusType? Lots of thanks

Alex