Those two buttons just completely cease all function, which means the campaign stops dead in its track, which sucks because this one used to be my favorite because of the length of the campaign and it really forces you to get clever with your resources.
Everything will be fine earlier in play, and then all of a sudden something triggers to cause the world map to stop functioning properly. It mostly seems to appear in the Athens Campaign later on, especially when the Persians unlock. I am bumping this post, as I appear to often have this same issue.
