You need the 9.1 No-CD patch for 9.1 which i have used trouble free since it was smuggled out! A lot of software no has on-line activation, which is better for not having to use CDs all the time, which I hate, but not so good if you want to run the software on several machines. However, I ran out of automatic web activations on FSX (you get 3) and if I move it again I'll have to get a second telephone activation. the first was given without hassle when I said I'd moved FSX onto a machine which couldn't run it and so moved it back again. Peter