Mac error code -50: what it means and how to fix it
Error -50 is one of the original Mac OS error numbers, paramErr, meaning an error in the parameter list: something about the request itself was invalid. In modern practice you meet it in the Finder while copying files, almost always to an external drive, a network share, or a disk image, and the copy stops with 'The operation can't be completed because an unexpected error occurred (error code -50)'. The parameters a drive rejects are usually about the files themselves, their names, their size, or a drive that fell asleep or disconnected mid-copy.
What causes it
- Filenames containing characters the destination format forbids, common when copying to FAT32 or network shares.
- A file larger than the destination format allows, FAT32's 4 GB ceiling being the classic.
- An external drive that sleeps, disconnects, or drops off the bus during a long copy.
- A failing drive or cable producing invalid responses the Finder reports as -50.
- Permissions or a nearly full destination making the copy parameters impossible.
Fix it, in order
- Identify the file that stops the copy. Copy the files in smaller batches. When a batch fails, split it again. The file that always fails carries the problem, usually its name or its size.
- Clean the filename. Rename problem files to plain letters, numbers, and hyphens. Remove slashes, colons, leading dots, and unusual symbols, then copy again.
- Check the destination's format. If it is FAT32, no single file over 4 GB can be copied, full stop. Reformat to exFAT (which erases the drive) or split large files.
- Keep the drive awake and connected. Use a direct connection instead of a hub, and on laptops stay on power. In Energy settings, preventing disk sleep during a long copy removes a whole category of -50s.
- Check the destination's free space and health. A copy to a nearly full or failing drive fails in exactly this vague way. Disk Utility's First Aid is the built-in check.
- Copy through a fresh path. Restarting the Mac and remounting network shares clears stale sessions that produce parameter errors against perfectly good drives.
Reformatting a drive erases it. The FAT32 fix above (exFAT) wipes everything on the destination. Move its contents somewhere safe first, and confirm twice which drive you are about to erase.
Common questions
Is error -50 a sign my drive is dying? It can be, but usually it is not. The common causes are filenames, file size versus format, and drives sleeping or disconnecting. A drive that produces -50 with many different files, cables, and computers is the pattern that suggests failing hardware, and Disk Utility First Aid plus the drive's SMART status will say more.
Why does the same file copy to one drive and fail on another? Because formats have different rules. A filename or a 5 GB video that a Mac-formatted drive accepts without comment violates FAT32's character and size rules. The file is legal on one destination and an invalid parameter on the other, which is precisely what -50 reports.
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