Plugin method call "NoSuchFieldError : actualValueType" exception

Hi all! I'm trying to develop a plugin to interact with Jena ( http://jena.sourceforge.net), a semantic web framework. I developed the plugin as I documented it in the plugin development tutorial. I have a hello() method which works perfectly. however when I try to call this method: public List<String> test1(){ Vector<String> uris = new Vector<String>(); OntModel model = ModelFactory.createOntologyModel( OntModelSpec.RDFS_MEM_RDFS_INF, null ); model.read(" http://www.dcs.shef.ac.uk/~zzc05jb/environmentOntology/pollutionInventory.r… "); model.read(" http://www.dcs.shef.ac.uk/~zzc05jb/environmentOntology/instances/disposalRe… "); Iterator iter = model.listIndividuals(); while(iter.hasNext()){ OntResource ontClass = (OntResource)iter.next(); uris.add(ontClass.getURI()); } return uris; } I get this exception: Error number 4001 in 4: Error while parsing velocity page Tests.OntologyPlugin Wrapped Exception: Invocation of method 'test1' in class secoia.plugin.OntologyPluginApi threw exception class java.lang.NoSuchFieldError : actualValueType I can't really make sense of it. This method works if i use it form a classic Java application. I copied all the Jena jar files to the webapps/xwiki/WEB-INF/lib directory. Moreover, I don't know where this actualValueType comes from. Does it come from XWiki? Any clue on this problem? Thanks a lot! -- _ _ Julien Bourdon (o)(o)--. http://purl.org/net/JulienBourdon \../ ( ) self isAddictedTo:(#Squeak&#linux) m\/m--m'`--. ^true