I downloaded some custom flat rides and buildings and when I go to use them, my game freezes and I get the error message.I read the readme's very carefully and made sure to install properly, I also extracted them into a temporary folder first, also tried extracting them directly into the folder.I removed them and tried again.Not working.

I've tried Shyguy's main street sets and those even freeze.

Download it again from another site. where did you download them from? Try the site we are on, it usually works for me.