403 Error v4 to v5

When trying to upgrade my v4 to v5 site I have followed the instructions by updating my v4 to the latest and setting up v5 separately and cron running.

When I go to migrate and put in the new URL I get a 403 Forbidden Access to this resource on the server is denied! message.

Any ideas?


Maybe the info here will help, also adding/removing the trailing slash may help