Are you re-running the same installer on the computer? The installer will just skip the product key screen if you're already activated.
Also, in the tutorial we talk about 2 methods: (1) letting the user skip the product key step and (2) forcing the user to activate immediately. Which method are you using?
Are you using cloned virtual machines?
Also, what are the flag options for CheckAndSavePKey?
The 2 flag options are TA_USER (== 2) and TA_SYSTEM (== 1). If you're using CheckAndSavePKey in installer then use TA_SYSTEM -- which is what we have in the example.