Provide informative error when connecting an older version of Dask (#4076)
Provide informative error when connecting an older version of Dask (#4076)

This seems to be coming up with the new protocol changes.
In the future we'll know which versions are present and so will be able
to give better messages.  This should stop the bleeding short term
though.
dask/distributed,dask/distributed,dask/distributed,dask/distributed