Does anyone know where i can download a version of VEX Cad from, or if it has to be bought where i can do that from?

Try here, CAD for VEX™ Robotics Kits.

I went to the site and downloaded the program and the parts and did everything that it told me to, but when i went to go to install it, it gave me this message…

Any solutions?

there are none it means who ever made that website made an error

For a class project in Engineering drawing and design we decided to recreate every part on our competition robot and put them together in Autodesk inventor 9. The week after we finished all these vex cad files came out. I wish I had read about them ahead of time it was hard to draw some parts like the servos and some of the screws. It looked good when we were done though.