OK. Used the cleaner on both PCs to wipe registry/files and start again. Still can't backup. New results...
Sony Vaio: XP Pro SP2
6.7.22 - Cable : 90% - Lost Connection Error.
6.7.22 - Bluetooth : 90% - Lost Connection Error.
6.81.13 - Cable : 90% - Lost Connection Error.
6.81.13 - Bluetooth : 90% - Lost Connection Error.
6.82.22 - Cable : Can't find Phone
6.82.22 - Bluetooth : Can't find Phone
Athlon XP x2 3800: XP Pro 64bit
6.7.22 - Cable : Not 64 bit compatible
6.7.22 - Bluetooth : Not 64 bit compatible
6.81.13 - Cable : 90% - Lost Connection Error.
6.81.13 - Bluetooth : 90% - Lost Connection Error.
6.82.22 - Cable : 90% - Lost Connection Error.
6.82.22 - Bluetooth : 90% - Lost Connection Error.
In every case, I rebooted both the PC and the phone to make sure a previous attempt didn't leave any problems.