Trying to import one 3.8.4 forum into another 3.8.4 forum. During users import for "Would you like to associated imported users with existing users if the email address matches ?" I select yes. Unfortunately instead of associating imported users with existing users if there is a matching email address ImpEx throws an error:

Invalid, skipping. Failed on :

What do I have to do to get this to work as advertised?