is there a fix for "vehicle design unavailable, ride performance may be affected" message?

[sweetnovabee]

I have this message on so many of the rides on my game, I'll attach a screenshot to show an example. 

Would love to know what this means / what causes it / how to fix it.

I use the Steam RCT1 (Deluxe) & RCT2 (Triple Thrill Pack), and have tons of downloaded custom made content... but I'm pretty sure all of the rides that display this message are the ones titled like "u(0489)" for example. 

Any help or guidance is greatly appreciated. Thanks in advance!!