Ok the exclusion works fine (no more unmarshal problem).... even if I don't include the dependency to jbosssx-client from org.picketbox group...
It seems there is an overlap of some dependency in my project... nor in the jboss 6 Final maven hierarchy.
Something strange is that even if I follow dependency tree from jboss-as-parent via jboss-as-security to jbosssx-client I don't find anywhere the version of jbosssx specified (3.0.0.CR2).
Thanks a lot for the tip.
Best regards, jérôme.