more JSF woes Cannot get value for expression

This is so difficult to troubleshoot, I am going at a snails pace.
Next issue.

I can go from the login page to a list of products page via a bean
method.

I duplicated the same code - but of course the next jsp doesnt work
with the following error:

javax.servlet.ServletException: Cannot get value for expression
'#{artifactTreeBean.artifactList}'
    javax.faces.webapp.FacesServlet.service(FacesServlet.java:121)
    org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:81)

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Where on earth is the originating error - not in the JBoss server.log,
thats the only error above.
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artifacttree.jsp
h:dataTable
    value="#{artifactTreeBean.artifactList}"
    var="artifact"

  <h:column>
        <f:facet name="header">
            <h:outputText value="Product" />
        </f:facet>
        <h:commandLink action="artifacttree">
            <h:outputText value="#{artifact.artifactName}" />
        </h:commandLink>
     </h:column>

</h:dataTable>

faces-config.xml
  <managed-bean>
    <managed-bean-name>artifactTreeBean</managed-bean-name>

<managed-bean-class>com.myproject.artifact.ArtifactTreeBean</managed-bean-class>
    <managed-bean-scope>session</managed-bean-scope>
  </managed-bean>

    <navigation-case>
      <from-outcome>artifacttree</from-outcome>
      <to-view-id>/pages/artifact/artifacttree.jsp</to-view-id>
    </navigation-case>

public class ArtifactTreeBean extends BaseBean {

    private List artifactList = null;

    public ArtifactTreeBean() {
        super();
    }
... populate the artifactList in the getter - should not throw an
error...