Improve CS resource not working

[gremlins0]

I am allied with a CS and they have coal and I don't. I want to use the option to improve the resource for 200, but it isn't letting me do it. I used this before, but for some reason it isn't a highlighted option. I am probably the first civ to discovery industrialsim. Do I have to wait until half the civs do it before the CS will let me improve their resource?

 

[DemonMaster]

Perhaps they don't know what coal is yet (e.g. they don't have the tech yet).

 

[Scott Jegg]

I think 50% of all civs need to have that tech before a CS can use it.

 

[Browd]

If the CS has already mined the coal tile, you can't pay 200 gold to improve it (since it's already improved), but you also won't get the coal until the CS "discovers" coal. If the coal tile is unimproved, you can pay the 200 gold and get the coal right away, even if the CS hasn't "discovered" coal (must think it's giving you dirty rocks and can't imagine why you wanted them so badly).

Same applies to any mined resource.