== Error -54 ==
From an OS9 reference, error -54 is a software lock on a file or a permissions error. (Some of the old codes still apply to OSX although there is no formal list of OSX error codes.)
First, try simply restarting your computer.
iTunes Library cannot be saved (Error -54) - https://discussions.apple.com/thread/1912814
Unknown error (-54) while syncing ipod - https://discussions.apple.com/thread/1082953 - problem was locked files
Why does iTunes keep showing a -54 error when I sync my iPad? - https://discussions.apple.com/thread/3727114
Error -54 possibly related to Touch Copy - https://discussions.apple.com/thread/3727114 - cleared by deleting preferences on iPad.