Help Mini image making speed



Hey there, I was reading cdkiller’s mini image tutorial because I wanted to make a mini image from a MechWarrior 4: Mercenaries ISO image from the original cd. When I tried to change the speed to 1x as the tutorial says, I couldnt, the speed option was locked in Maximum speed. I need someone to tell me how do I fix this or if I have to make a mini image from the original cd and not from an ISO. Thanks.