iTunes error 45054 comes up due to permissions issues on the disk. This can happen with time when other programs changes permissions and can be easily repaired and fixed. This guide points to DiskWarrior but you can also use CCleaner for Mac or Disk Utility to repair permissions.
DiskWarrior 5 supports any locally connected Mac OS Standard (HFS) or Mac OS Extended (HFS Plus) disk including Fusion Drives, RAID volumes, journaled disks, case-sensitive disks, FileVaults and Time Machine backups. DiskWarrior 5 supports both PowerPC and Intel Macs started in OS X 10.5.8 through 10.10.
You can download DiskWarrior from http://www.alsoft.com/
Using DiskWarrior is easy, just download it and open it. You will see the options listed on the program’s console to repair/rebuild permissions.