Playing RCT1 scenarios. Seemingly at random (though it may be after a certain time in a scenario) all my rides become free and the option becomes greyed out. I have not set a park admission price, so there is no reason I shouldn't be able to charge for rides. Reloading doesn't help.
The odd thing is that even if I load an old autosave (where I know charging for rides was working) it's still showing as Free with the option greyed out. So it seems to be a bug with the game that is not tied to the saved game file.
