I keep getting this message with many rides:

"ride includes scenery which is unavailable"

That happens when you're trying to build a ride that has in-built scenery that is not enabled in that specific scenario.

Each scenario has a set of scenery (and rides) that are available. Some rides have attached scenery that may be selectively turned on and off (IIRC), but if that scenario doesn't have the necessary scenery (e.g. Space Themeing, and you're playing, I don't know, the Great Wall of China scenario), the scenery will forcefully be removed.

Try out the scenario editor to familiarize yourself with this concept.


(for Google-ers, this is for RCT2)