 <p>That usually happens when trying to use a model that was trained for a different tagger version. Make sure you are using the models distributed with the 3.3.1 tagger.</p> <p>I faced the same problem once. Then I realized that the jar version I was using was from 3.3.1 release. And the model was from 3.2.0. I removed the 3.2.0 model files and replaced them with 3.3.1.</p> <p>Hope this helps.</p>