java.lang.NullPointerException using Schema Compliance Asser

Hi,

I am trying to use the 'Schema Compliance Assertion' in one of our test cases. This is the scenario:

1) I call a service and get some XML response (using WADL)
2) The response of this service is checked with a 'Schema Compliance Assertion'

The assertion of the assertion generates an error though:

Mon Feb 14 17:25:56 CET 2011:ERROR:java.lang.NullPointerException
   java.lang.NullPointerException
    at com.eviware.soapui.impl.wadl.WadlDefinitionContext.createDefinitionLoader(WadlDefinitionContext.java:52)
    at com.eviware.soapui.impl.support.definition.support.AbstractDefinitionContext$Loader.getDefinitionLoader(AbstractDefinitionContext.java:198)
    at com.eviware.soapui.impl.support.definition.support.AbstractDefinitionContext$Loader.construct(AbstractDefinitionContext.java:218)
    at com.eviware.soapui.support.swing.SwingWorkerDelegator.construct(SwingWorkerDelegator.java:46)
    at com.eviware.soapui.support.swing.SwingWorker$2.run(SwingWorker.java:140)
    at java.lang.Thread.run(Unknown Source)

Are there additional steps I need to take to be able to use the schema assertion?

thanks!

(we are running SoapUI 3.6.1)