Secure Loader error

I purchased Space Interceptor for my son. Nice fluent process via PayPal. I downloaded the game with my computer and installed it on his computer. Now the game won't start up. It gives me an error about something called Secure Loader.

If I install the game on the machine that I downloaded it with, I don't get the error. I get a window with Activation options. But I don't want to play the game on this machine. I want it on the other machine.

Does anyone know how to fix this?

(I really hate security measures that punish legitimate customers more than pirates... :( )

Downloaded the game again with the machine I want to install it on. To no avail.

Installed the game on a third machine (also XP Pro like the final machine I want the game on). Here it works: I get the Activation window.

Could I activate the game on one machine and then run it on another?

The machine where it works has XP Pro SP 2. The one where I get the error has SP1. This was also the machine where I had installed the game demo before.

I fixed it.

Logging into the Administrator account on that machine, then running the prv_setup.exe file that was installed with the game and then running the game. Then I got to see the Activation screen.

Pity the game did not come with these instructions.
Next time I'll think twice before paying for a game and check the torrent sites first.