When you say you're trying to "download MM-17 to my 2nd PC", does that mean you already have it downloaded to another (1st) computer? Or, did you purchase a "second seat"?
As I suspected, you are attempting to load the same program on two different machines. If you had read the End User's License Agreement (EULA) when you installed MMM, you would know that is not allowed.
You can have the program on only one computer at a time, unless you purchase TWO licenses. So, you either have to uninstall it from your laptop first and then install on your PC, OR purchase another instance of the program for your desktop (PC).