SQL error when adding flag link in view of users having flagged comments

Getting the following error message

user warning: Unknown column 'users.cid' in 'field list' query: SELECT users.uid AS uid, content_id, users.cid AS users_cid FROM users users INNER JOIN flag_content flag_content_users ON users.uid = flag_content_users.uid AND flag_content_users.fid = 2 LIMIT 0, 10 in (yada yada)/modules/views/includes/view.inc on line 731.

when adding Flags: Flag link to the fields list in a view of users with the relationship "Flags: User's flagged content". Other fields don't give errors. They don't give results either but that might be me.

Using Views 6.x-2.5