Odd, i have never had it blue screen before.
The program calls the regsave api and Windows writes the registry to a new file. Just like it would with any other database, and thats how the file becomes smaller from the bloat. So normally this should be just fine.
But just like a database, if there is something correct inside of it, or if part of the new registry file is landing on a bad sector on the drive then that would also cause a problem, even a blue screen depending.
Have you used the program called "WhoCrashed" and use it to see if it can see what caused the blue screen? Do you happen to have the error msg and number of the blue screen as well so i can look it up?
Shane