Registration Changer alert box on registering Arcgis

Hi guys, my post here is about my problem in registering arcgis, when I register the application an error message appeared on my screen, somewhat a strange message, "You must select an operating system", please refer below the pasted screen shot of the error message for you reference.
You must select an operating system!
As I read on the error, I am deeply troubled, why it generated this error, even though I selected an operating system, this error message will pop up, I am also thinking for an application error, or the registration module has a bug,
Please share you idea on this matter,
Thanks a lot.
