Q: iTunes library fileb cannot be saved 54

Telling us what you were doing might narrow it down.

From an OS9 reference, error -54 is a software lock on a file or a permissions error. (Although there is no formal list of OSX error code some of the old codes still apply to OSX .)

First, try simply restarting your computer.

Try quitting iTunes, then deleting the .xml (not .itl !) version of the library file in the iTunes folder (iTunes will generate a new one).

iTunes Library cannot be saved (Error -54) - https://discussions.apple.com/thread/1912814 - various things to try.

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.

iTunes: Missing folder or incorrect permissions may prevent authorization - http://support.apple.com/kb/ts1277

Troubleshooting permissions issues in Mac OS X - http://support.apple.com/kb/HT2963