I have only been a Mac user since Jan of 2010 and really like it. However for the last 2 weeks time machine was stuck in calculating changes and lock up the computer so I could not do a shut down or restart without pressing the power button. After "hard booting" the computer, time machine would work properly again until the evening when it would co into the calculating changes again. I would get error messages 22, and then error 36. After going through the troubleshooting steps at the top of the section (changing from firewire to USB, and Resetting time machine) all seems well again. Thanks for the posting of the troubleshooting steps and being a new user I find this forum invaluable.