@Vinnz,
I'm not sure but there may be a problem with a melee unit attacking out of a city that also has a GP in it. Can you confirm that that is the exact problem?
I confirm (but I didn't see by myself that the GP was involved).
I just tried again from the save.
My warriors can't attack out of the city when the GP (an engineer) is on the same tile. As soon as I move the GP out, the warriors can attack.