How to pass a caught error from one .cs file to output in a textbox in another .cs file? (same sln)

I have two classes that i'm working with. I'm trying to catch an error in one class and output that to a textbox that exists in another class. In my example I'm trying to make my Circle method throw a caught error to my ErrorOutputWindow in my windows form called BooseForm. I think this is a pretty simple implementation but I may be wrong?

All help appreciated, thank you!