NOTE: I am using Python 2.7 as part of Anaconda distribution. I hope this is not a problem for nltk 3.1.
I am trying to use nltk for NER as
import nl
The best thing to do is simply to download the latest version of the Stanford NER tagger where the dependency problem is now fixed (March 2018).
wget https://nlp.stanford.edu/software/stanford-ner-2018-02-27.zip