Random Forests using org.apache.mahout.classifier.df.* lib

Sometimes correct, sometimes the following error appears
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1
at
org.apache.mahout.classifier.df.DecisionForest.classify(DecisionForest.j
ava:112)
at
feiyu.com.kaggledigitrecognizer.RandomForestsSolution.main(RandomForests
Solution.java:86)