Classifieds author search not working

I've got the Classifieds plugin installed.
When I view a single classified, the author has a hyperlink, in the same way as the categories has. When I click on the author link in the 'posted by' field, it just says 'nothing found'.
An example of a classified:
http://innovationdistricts.org/listing/agriprotein-technologies-ltd/

Can you please advise?

thanks