error while converting from nt to rdf/xml format in Jena

Question

What is the meaning of the following error message: I am attempting to convert the dogfood.nt to its rdf/xml representation form, what does the StackOverflow message indicate ?

<j.12:Person rdf:about="http://data.semanticweb.org/person/rich-keller">
   <j.12:name>Rich Keller</j.12:name>
   <rdfs:label>Rich Keller</rdfs:label>
   <j.3:affiliation rdf:resource="http://data.semanticweb.org/organization/nasa-ames-research-center"/>
   <j.4:holdsRole rdf:resource="http://data.semanticweb.org/conference/iswc/2005/pc-member-at-iswc2005-research-track"/>
   </j.12:PersException in thread "main" java.lang.StackOverflowError
       at java.util.regex.Pattern$BranchConn.match(Pattern.java:4568)
       at java.util.regex.Pattern$GroupTail.match(Pattern.java:4717)
       at java.util.regex.Pattern$BranchConn.match(Pattern.java:4568)
       at java.util.regex.Pattern$GroupTail.match(Pattern.java:4717)
       at java.util.regex.Pattern$Curly.match0(Pattern.java:4272)
       at java.util.regex.Pattern$Curly.match(Pattern.java:4234)
       at java.util.regex.Pattern$GroupHead.match(Pattern.java:4658)
       at java.util.regex.Pattern$Branch.match(Pattern.java:4604)
       at java.util.regex.Pattern$GroupHead.match(Pattern.java:4658)
       at java.util.regex.Pattern$Branch.match(Pattern.java:4604)
       at java.util.regex.Pattern$Branch.match(Pattern.java:4602)

Following is the code snippet used:

Model model11 = ModelFactory.createDefaultModel();
        InputStream is1 = FileManager.get().open("dogfood4.nt");

        if (is1 != null) {
            model11.read(is1, null, "N-TRIPLE");

            model11.write(os1, "RDF/XML");
        } else {
            System.err.println("cannot read file ");;
        }

I am using the semantic dogfood n-triples.