dbpedia - SPARQL federated query "SERVICE" returns Virtuoso RDFZZ Error: unexpected variable name 'stubvar14' -

dbpedia - SPARQL federated query "SERVICE" returns Virtuoso RDFZZ Error: unexpected variable name 'stubvar14' -

i want list of persons 2 different sparql-endpoints, i'm using query on de.dbpedia:

prefix category-en: <http://dbpedia.org/resource/category:> select distinct * { ?name dcterms:subject category-de:haus_liechtenstein. ?name rdf:type foaf:person. service <http://dbpedia.org/sparql> { ?name dcterms:subject category-en:princely_family_of_liechtenstein. ?name rdf:type foaf:person. } minus {?name dbpedia-owl:deathdate ?d} }

i next error:

virtuoso rdfzz error db.dba.sparql_rexec('http://dbpedia.org/sparql', ...) has received result unexpected variable name 'stubvar14'

any thought i'm doing wrong? lot!

so problem although both these queries work fine separately, service part in combined query trying filter first set based on sec set. think missing union:

prefix category-en: <http://dbpedia.org/resource/category:> select distinct count(?name) { { ?name dcterms:subject category-de:haus_liechtenstein. ?name rdf:type foaf:person. } union{ service silent <http://dbpedia.org/sparql>{ ?name dcterms:subject category-en:princely_family_of_liechtenstein. ?name rdf:type foaf:person. } } minus {?name dbpedia-owl:deathdate ?d} }

sparql dbpedia