Wikidata SPARQL aficionados,

This SPARQL query worked for several weeks, but quit working a few days ago:

PREFIX rdfs: http://www.w3.org/2000/01/rdf-schema# PREFIX wikibase: http://wikiba.se/ontology# PREFIX entity: http://www.wikidata.org/entity/ PREFIX p: http://www.wikidata.org/prop/direct/

SELECT ?propUrl ?propLabel ?valUrl ?valLabel WHERE { hint:Query hint:optimizer 'None' . entity:Q42 ?propUrl ?valUrl . ?valUrl rdfs:label ?valLabel

FILTER (LANG(?valLabel) = 'en') .

?property ?ref ?propUrl . ?property a wikibase:Property . ?property rdfs:label ?propLabel

FILTER (lang(?propLabel) = 'en' ) } ORDER BY ?propUrl ?valUrl LIMIT 100

Here is the first part of the exception:

java.util.concurrent.ExecutionException: java.util.concurrent.ExecutionException: org.openrdf.query.QueryEvaluationException: java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.Exception: task=ChunkTask{query=7be8b715-1429-4348-bf97-237d06d6084c,bopId=17,partitionId=-1,sinkId=19,altSinkId=null}, cause=java.util.concurrent.ExecutionException: java.lang.RuntimeException: com.bigdata.rdf.internal.NotMaterializedException: Vocab(6)

Any ideas on how I can modify the query to work again?

Please advise, James Weaver