Faulty Achievements

I've played Civ V for hundreds of hours, so I know that I could have earned these achievements many times over. For some reason though, they simply aren't going through. Is this a common problem?

The achievements are:
Land Barron - Buy 1000 Tiles
The Explorer - Discover 100 Natural Wonders
The Appian Way - 1000 Roads
Forty-Niner - 1000 Mines
Paul Bunyan - Chop down 1000 Forests
God is Great - 1000 Temples

Anybody know of any fixes?

Do you use any mods? You don't get achievements for modded games.