title: Weka says 'training and test set are not compatible' when both are the same file
body: <p>I'm getting a very odd error from the weka machine learning toolkit:</p>
  
  <pre><code>java weka.classifiers.meta.AdaBoostM1 -t train.arff -d tmp.model -c 22 //generates the model
  java weka.classifiers.meta.AdaBoostM1 -l tmp.model -T train.arff -p 22 //have the model predict values in the set it was trained on.
  </code></pre>
  
  <p>This produces the message:</p>
  
  <pre><code>java.lang.Exception: training and test set are not compatible
          at weka.classifiers.Evaluation.evaluateModel(Evaluation.java:1035)
          at weka.classifiers.Classifier.runClassifier(Classifier.java:312)
          at weka.classifiers.meta.AdaBoostM1.main(AdaBoostM1.java:779)
  </code></pre>
  
  <p>But of course, the input files are the same... Any suggestions?</p>