I've just updated to the latest version and the discussion link isn't showing (the discussion thread wasn't a feature of the version I upgraded from).
There doesn't seem to be any usegroup permissions for viewing the discussion tab but I'm thinking it might be related to some edits I made to the tabs to merge them all into one but I'd have expected that to be overwritten when I upgraded...?
There doesn't seem to be any usegroup permissions for viewing the discussion tab but I'm thinking it might be related to some edits I made to the tabs to merge them all into one but I'd have expected that to be overwritten when I upgraded...?