Q&A Visitors can't vote without being registered

Hi - I've just installed the Q&A plugin. I have set up visitors to have all privileges (we are going to be using it on an internal network)I have also set it up so that a question is assigned to a user. Everything works fine for logged out users except when they try and vote on an answer it says please log in or register to vote. How can I set it up so that visitors can also vote on answers / questions without being logged in? - Thanks