Relay takes advantage of all permissions roles. In the Content & Sharing tab of your Enterprise Settings, verify that the all permission roles are checked in the Collaborating on Content section:
Note: Settings in the Custom Setup tab (e.g. Custom Sub-domains or Branding modifications) will not interfere with Relay, though Relay will not capture these settings.
End User Account Settings
Relay adds users in a workflow as collaborators in folders containing the workflow's content. This way, the content is always available to everyone in a given workflow. We recommend that all users auto-accept collaboration invites to folders so that they can easily be assigned work in Relay. This setting can be found in the Sharing tab of a user's Account Settings.