I have been using a MyBook WD 1TB drive connected to my AirPort Extreme for my TimeMachine back up disc. I have noticed that it has not been backing up recently so I made sure to open open the drive and have it mounted to my desktop then clicked "Back Up Now" on the TM pull down menu, it said "Preparing Backup" in the TM Pref screen then came back with the notification "The backup disc is not available" even though I know it should be since the icon is on my desktop. The only change I have made recently is updating my system to Snow Leopard but I'm not sure exactly if that was when my back ups stopped. Can anyone help me with this issue I'm having?????