title: java.lang.IncompatibleClassChangeError, BM25BooleanQuery
body: <pre><code>Exception in thread "main" java.lang.IncompatibleClassChangeError: Implementing class
      at java.lang.ClassLoader.defineClass1(Native Method)
      at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
      at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
      at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
      at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
      at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
      at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
      at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
      at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
      at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
      at NVoting.&lt;init&gt;(NVoting.java:143)
      at Main.main(Main.java:8)
  </code></pre>
  
  <p>on this line:</p>
  
  <pre><code>booleanQuery.add(new BM25BooleanQuery(current_tags[i], 
                              "tags",
                              new StandardAnalyzer(org.apache.lucene.util.Version.LUCENE_31)), 
                              BooleanClause.Occur.SHOULD);
  </code></pre>
  
  <p>I'm using an implementation of BM25 Okapi retrieval system: <a href="http://nlp.uned.es/~jperezi/Lucene-BM25" rel="nofollow">http://nlp.uned.es/~jperezi/Lucene-BM25</a></p>
  
  <p>Can you help me to fix the issue ? I'm using Lucene 3.1
  I've also tried Lucene 2.9.4 with no luck.</p>
  
  <p>thanks</p>