HTTPException:500 exception while executing a federated SPARQL query with Jena ARQ

[June]

Dear list,

I am trying to perform a federated SPARQL query by Jena arq for the 
first time, and I am using the latest version of Jena.

But I encountered a HTTPException:500 exception for executing the 
following query. It will be very helpful if you can give me some tips 
about this problem.

PREFIX  drugbank: 
<http://wifo5-04.informatik.uni-mannheim.de/drugbank/resource/drugbank/>
PREFIX  sider: 
<http://wifo5-04.informatik.uni-mannheim.de/sider/resource/sider/>
PREFIX  owl:  <http://www.w3.org/2002/07/owl#>
PREFIX  rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#>

SELECT  ?drug ?enzyme
WHERE
  { ?drug rdf:type drugbank:drugs .
    ?drug drugbank:enzyme ?enzyme .
    ?enzyme rdf:type drugbank:enzymes
    SERVICE <http://wifo5-04.informatik.uni-mannheim.de/sider/sparql>
      { ?drugInSider owl:sameAs ?drug .
        ?drugInSider rdf:type sider:drugs .
        ?drugInSider sider:sideEffect ?sideEffect .
        ?sideEffect rdf:type sider:side_effects
      }
  }
LIMIT   10

The codes I am using are:

  val query = QueryFactory.create(qStr)
  val qexec = 
QueryExecutionFactory.sparqlService("http://wifo5-04.informatik.uni-mannheim.de/drugbank/sparql";, 
query)
  try {
    val results = qexec.execSelect()
    while (results.hasNext()) {
      val result = results.next
      println(result.get("drug") + "\t" + result.get("enzyme"))// + 
"\t" + result.get("sideEffect"))
    }
  } finally {
    qexec.close();
  }

Many thanks!

Best wishes,

June