session-context:authentication not working... why?

[Antonio Fiol Bonnín]

Does anyone see why this tells me that:

org.apache.excalibur.source.SourceException:  The attribute: authentication/authentication/data is empty

<map:act type="auth-protect">
    <map:parameter name="handler" value="auth-handler"/>
    <map:generate src="" />
    <map:serialize />
</map:act>

Thank you very much.

--
Antonio