Use of configuration-point to inject a service-point

Are those configurations equivalent ?

1.
    <service-point id="RubricHierarchyFactory"
interface="org.apache.tapestry.engine.state.StateObjectFactory">
        <invoke-factory>
            <construct
class="com.cariboonetworks.ads.services.impl.RubricHierarchyFactory">
                <set-object property="root" value="service:RubricAd"/>
            </construct>
        </invoke-factory>
    </service-point>

2.
    <service-point id="RubricHierarchyFactory"
interface="org.apache.tapestry.engine.state.StateObjectFactory">
        <invoke-factory>
            <construct
class="com.cariboonetworks.ads.services.impl.RubricHierarchyFactory">
                <set-configuration property="root"
configuration-id="RubricRoot"/>
            </construct>
        </invoke-factory>
    </service-point>

    <configuration-point id="RubricRoot">
      <schema>
        <element name="rubric">
          <attribute name="service-id" translator="service-point"
required="true" unique="true"/>
        </element>
      </schema>
    </configuration-point>
   
    <contribution configuration-id="RubricRoot">
        <rubric service-id="RubricAd"/>
    </contribution>

In the second one, it returns :
"Unable to update property root of
com.cariboonetworks.ads.services.impl.RubricHierarchyFactory@1052a203:
argument type mismatch"
and i don't understand why ...

Thanks in advance for any clue.

Stephane