Does anyone know to what this RedFace issue refers to?

I've never noticed it in past games of Civ 4, but I've just started my first proper game of Beyond the Sword. Maybe thats it. Or, maybe its my mod - I'm running the latest version of Rise of Mankind at the moment.

Still, its a strange one. What causes "We long for the open country!", and is there a way of getting rid of it?

Never heard of it. Must be part of the mod. Perhaps it's just a revamped "It's just way too crowded!" red face?

Never got that one, i'd say it's probably due to your mod.

I think it may be part of barbarism...

It may be a side effect of the MOD, but it seems to be present in the Vanilla file, under the name ANGER_BIG_CITY.

If I'm translating the code correctly, it should appear if the player is running a civic that creates unhappy faces in his largest cities; in other words, something that boosts unhappy the same way that representation boosts happy.

Does that help?

Edit: the labor civic Mechanized Workforce from Final Frontier has this effect.