weird java / sEvaluate problem

Hello,
I am using PowerLoom via the java interface and currently am running 
into some problems when using the PLI.sEvaluate method. If i try to 
evaluate this command :

(retrieve all (and (subset-of surfboard ?x) (subset-of wetsuit ?x)))

i get an exception like this :

Exception in thread "main" edu.isi.stella.StellaException: Invocation 
Target Exception in funcall of function:
     public static edu.isi.powerloom.logic.QueryIterator 
edu.isi.powerloom.logic.Logic.retrieveEvaluatorWrapper(edu.isi.stella.Cons) 
((ALL (AND (SUBSET-OF @SURFBOARD ?X) (SUBSET-OF @WETSUIT ?X))))
     java.lang.NullPointerException
     null
java.lang.NullPointerException
     at 
edu.isi.powerloom.logic.Logic.helpSelectRelationPropositions(Logic.java:11560)
     at 
edu.isi.powerloom.logic.Logic.selectRelationPropositions(Logic.java:11727)
     at edu.isi.powerloom.logic.Logic.selectPropositions(Logic.java:11439)
     at 
edu.isi.powerloom.logic.Logic.allTrueDependentPropositions(Logic.java:28506)
     at 
edu.isi.powerloom.logic.Logic.helpMemoizeAccessBinaryValue(Logic.java:28832)
     at edu.isi.powerloom.logic.Logic.accessBinaryValue(Logic.java:28872)
     at 
edu.isi.powerloom.logic.NamedDescription.lookupSpecialist(NamedDescription.java:1119)
     at 
edu.isi.powerloom.logic.NamedDescription.inferableThroughBySomeDescendantP(NamedDescription.java:568)
     at 
edu.isi.powerloom.logic.Description.inferableWithCycleCheckP(Description.java:461)
     at edu.isi.powerloom.logic.Description.inferableP(Description.java:411)
     at 
edu.isi.powerloom.logic.Logic.inferableDescriptionP(Logic.java:25241)
     at 
edu.isi.powerloom.logic.ControlFrame.tryImpliesProof(ControlFrame.java:1521)
     at 
edu.isi.powerloom.logic.ControlFrame.executeProofStrategy(ControlFrame.java:2487)
     at 
edu.isi.powerloom.logic.ControlFrame.continueCurrentOrNextStrategy(ControlFrame.java:2658)
     at 
edu.isi.powerloom.logic.ControlFrame.continueStrategiesProofs(ControlFrame.java:2776)
     at 
edu.isi.powerloom.logic.ControlFrame.evaluateNextMove(ControlFrame.java:4710)
     at 
edu.isi.powerloom.logic.QueryIterator.executeBackwardChainingProofP(QueryIterator.java:1934)
     at edu.isi.powerloom.logic.QueryIterator.nextP(QueryIterator.java:1402)
     at edu.isi.powerloom.logic.Logic.callRetrieve(Logic.java:16834)
     at edu.isi.powerloom.logic.Logic.retrieve(Logic.java:16956)
     at 
edu.isi.powerloom.logic.Logic.retrieveEvaluatorWrapper(Logic.java:16964)
     at sun.reflect.GeneratedMethodAccessor21.invoke(Unknown Source)
     at 
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     at java.lang.reflect.Method.invoke(Method.java:597)
     at edu.isi.stella.javalib.Native.funcall(Native.java:566)
     at edu.isi.stella.Cons.evaluateConsTree(Cons.java:8560)
     at edu.isi.stella.Stella_Object.evaluate(Stella_Object.java:4968)
     at edu.isi.powerloom.PLI.evaluate(PLI.java:4549)
     at edu.isi.powerloom.PLI.sEvaluate(PLI.java:4592)
     at 
k.MAThesis.IE.tools.powerloom.PowerLooming.sEvaluate(PowerLooming.java:633)
     at 
k.MAThesis.IE.tools.powerloom.similarity.SimilarityCalculatorDice.calculateSimilarity(SimilarityCalculatorDice.java:58)
     at 
k.MAThesis.IE.tools.powerloom.similarity.TestSimilar.main(TestSimilar.java:27)

     at edu.isi.stella.javalib.Native.funcall(Native.java:610)
     at edu.isi.stella.Cons.evaluateConsTree(Cons.java:8560)
     at edu.isi.stella.Stella_Object.evaluate(Stella_Object.java:4968)
     at edu.isi.powerloom.PLI.evaluate(PLI.java:4549)
     at edu.isi.powerloom.PLI.sEvaluate(PLI.java:4592)
     at 
k.MAThesis.IE.tools.powerloom.PowerLooming.sEvaluate(PowerLooming.java:633)

If I, however, try to evaluate this command using the PLI command line, 
it shows to be no problem and gives the correct results. Does someone 
have a hunch on where this might root from?

thanks already,
Kalle Fischer