Starting up iTunes on my Windows 8.1 computer to sync iPhone 4 via USB immediately brings up the error message:
The iPhone can't be synced. An unknown error occurred (-54)
Any ideas how to overcome the error?
Error -54 is a file permissions issue.
Here are a couple of methods to reset common errors...
Fix the iTunes folder permissions
Open the Start menu & type %userprofile% (including both % symbols) then hit Enter you should see the My Music folder, which is the default location for iTunes music files.
Open My Music, select the iTunes folder
Then, make sure you have sufficient control over the contents of that folder -
Try your sync again…
Additional method, if the first doesn't work…
Restore TrustedInstaller permissions
Update June 2016
Apparently, the layout of the perms windows has changed in Win 8 & later - see
Set Folder Permissions in Windows 8 or 8.1 Computer or
How to Take Full Ownership of Files & Folders in Windows 8 / 10 for further info.
There is a utility called Windows Repair (All-in-One) by tweaking.com which I would highly recommend for a non-expert way to ensure Windows has all its correct defaults.
It is not any kind of "go-faster" tool, it doesn't speed up your machine in some 'magical' way. It just makes sure everything is as it should be. It won't break anything, so long as you follow the instructions precisely.
The free version is all you need, though personally I bought the pro version just to reward the author. [I have no affiliation, it's just saved my neck enough times to be worth recommending]
I ran into this problem with permissions on my daughter's phone. Restrictions was enabled and that made this error when trying to sync.
Much appreciate your efforts to help, but as noted in many posts, Windows 10 goes through the motions of changing the file 'read-only' attribute but refuses to actually do so.
In my case, the sync errors only occurred when I had my contact manager (MS Outlook) running, so it was locking the files.
Exit Outlook, run iTunes to do the sync, and problem solved.