How do I retrieve a JMS Security exception object in SoapUI?

I am sending a trying to read from a JMS queue ( Apache ActiveMQ), but I have invalid username/password combo. The broker responds with a JMSSecurityExceptions object, that is processed by the SoapUI source code and I get the message body form the exception object in the JMS Status assertion, but the assertion fails. I want to create a script assertion, that retrieves the object and parses the message from the object, and if it contains something like "user/pass invalid", the assertion should pass.