internalCategoryId is not a valid property for ProjectArea creating a work item

I want to create a work item with this code:

POST https://jazz.net/sandbox06-ccm/oslc/contexts/_1xR_IKcWEeKrmbBYQFHasd/workitems

<rdf:RDF
xmlns:dcterms="http://purl.org/dc/terms/"
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:rtc_cm="http://jazz.net/xmlns/prod/jazz/rtc/cm/1.0/" >
<rdf:Description rdf:nodeID="A0">
<rtc_cm:filedAgainst rdf:resource="https://jazz.net/sandbox06-ccm/resource/itemOid/com.ibm.team.workitem.Category/_1xR_IKcWEeKrmbBYQFHasd"/>
<dcterms:title rdf:parseType="Literal">Sample Work Item</dcterms:title>
<rtc_cm:type rdf:resource="https://jazz.net/sandbox06-ccm/oslc/types/_1xR_IKcWEeKrmbBYQFHasd/defect"/>;
</rdf:Description>
</rdf:RDF>

but the server responses:

status code 500

internalCategoryId is not a valid property for ProjectArea

what I am doing wrong?

thanks