I have an Airport Extreme (N) with a MyBook attached. When Leopard came out I hooked the disk up to my 12" PowerBook for the first backup and then moved it to the Airport for subsequent backups. This set up has always worked. However, I tried to do the same exact thing with my girlfriend's 15" MBP and it backs up over USB but will fail over Airport no matter what. Any tips? Anything I left out that would make a difference in the answer?