One possibility is that you might already be building it in another city. (It has been true in other posts.)
Check puppets (if you have any). If they truly run out of other things to build, they can (on rare occasions) start on projects that you would prefer they not build.
I have quite a few puppets. Several of them don't seem to be building anything at all. I wonder if there could be some sort of glitch there.
Anyway thanks again for the help. I guess I'll just play through and hope I don't run into it next time.
Did you mouse over the Manhattan Project? It might tell you why you can't build it(I can't remember if projects do that or not).
My reputation-decay with city-states is higher than it has been in other games, is that because I've captured a couple of city-states? Does the decay get greater with every one I dow/capture? Does the penalty itself decay over time?
Also, say I have two units to attack another unit (or city, whatever); one has a bonus, the other doesn't. Is there a better way around to do the attacks? Stronger then weaker, or weaker then stronger? If that makes sense.
Thank you! I meant to ask some other things though.
Do medics' or great generals' abilities stack? And can you use enemy roads when invading?