Can I only use locked keys to register my application?

Yes. To create locked license keys, you have to specify the machine ID before creating a new license key (License Manager). If you want to make sure that your application will only accept machine locked license keys, you can force WinLicense to check for them. To do so you have to go to the Registration panel and check the option Allow only hardware dependent (locked) registrations.

Please, go to the following KB entry.