WCF custom binding/extensions causes validation error in app.config

<system.serviceModel>

    <services>
        <service name="Zed.Apache.NMS.WCF.Test.Server.TestApacheNMSService">
            <endpoint
                name="nmsServiceEndpoint"
                address="tcp://localhost:61616"
                binding="nmsBinding"
                bindingConfiguration="defaultNmsBinding"
                contract="Zed.Apache.NMS.WCF.Test.Server.ITestApacheNMSService" />
        </service>
    </services>

    <bindings>
        <nmsBinding> <!-- VALIDATION ERROR HERE -->
            <binding name="defaultNmsBinding"
                     destination="TestApacheNMSQueue"
                     destinationType="Queue" />
        </nmsBinding>
    </bindings>

    <extensions>
        <bindingExtensions>
            <add name="nmsBinding"
                 type="Apache.NMS.WCF.NmsBindingCollection, Zed.Apache.NMS.WCF, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
        </bindingExtensions>
    </extensions>

</system.serviceModel>