Error installing Orbeon in JBoss

Deployment "vfsfile:/apps/jboss-6.0.0.20100216-M2/server/atlasit/deploy/orbeon.war/" is in error due to the following reason(s): java.lang.LinkageError: loader constraint violation in interface itable initialization: when resolving method "org.orbeon.saxon.xpath.XPathEvaluator.getNamespaceContext()Ljavax/xml/namespace/NamespaceContext;" the class loader (instance of org/jboss/classloader/spi/base/BaseClassLoader) of the current class, org/orbeon/saxon/xpath/XPathEvaluator,and the class loader (instance of <bootloader>) for interface javax/xml/xpath/XPath have different Class objects for the type javax/xml/namespace/NamespaceContext used in the signature

Any idea how to solve it?

Thanks a lot

Isi