I think it is a copy protection. But there is a cracked version, it tells you in the cracker-intro how to pass the copy protection doors.
But only one of the cracks (100% version or whatever will let you pass also the other copy-protection doors leading to the save points later in the game)
Anybody have a hint, I wonder what UAE settings to use to make that game as smooth as possible?
It was super sluggish back then even on my A1200...