XACML <PolicySetIdReference>

Hi, 

I've tried several ways of getting the <PolicySetIdReference> work, but I
still get the following error in my java program: 
<Response> 
<Result>
<Decision>Indeterminate</Decision> 
<Status>
 <StatusCode Value="urn:oasis:names:tc:xacml:1.0:status:processing-error"/> 
 <StatusMessage>couldn't resolve policy ref</StatusMessage> 
</Status> 
</Result> 
</Response>

I think with the following XML Expression it has to work: 
 
<PolicySetIdReference>urn:oasis:names:tc:xacml:1.0:example:policysetid:1</Po
licySetIdReference>

What do you think? 
Is there another way to reference to other Policies or PolicySets?

Thanks for your help
NK