MacBook Finder Error Code -36 — Cannot Read or Write Data Fix

What it means

MacBook error -36 is a macOS Finder I/O error.
The Finder's exact dialog reads: 'The Finder can't complete the operation because some data in [filename] can't be read or written.'
It appears when copying or moving files — most often when the source or destination is an external drive, a network share, or a removable USB stick.
The Finder hit a read or write that didn't complete and gave up on the whole operation rather than leaving half a copy behind.

Affected Models

Every MacBook running macOS (Finder is part of macOS, not a specific hardware model)
Common on copies to or from USB flash drives and external SSDs
Common on copies to or from network shares (SMB, AFP)
Common on copies involving folders that travelled through Windows machines (stray .DS_Store metadata)
Affects every recent macOS — Sequoia, Sonoma, Ventura, Monterey, Big Sur, and earlier

Common Causes

External drive read error on one of the files inside the folder being copied
Hidden .DS_Store metadata file got corrupted on a non-Apple filesystem
Filesystem of the destination doesn't support a feature one of the source files uses (resource forks, extended attributes)
USB cable or port intermittently disconnecting mid-copy
Failing sector on the source drive — repeatable -36 on the same file is a strong signal

How to Fix It

Re-seat the external drive's cable.

If the error happened during a copy to or from an external drive, unplug the drive and plug it back in firmly.
A loose USB-C or Thunderbolt cable causes intermittent disconnects that show up as -36.
Try a different USB port if the same cable still fails.
Run dot_clean on the source folder.

Open Terminal and run: dot_clean ~/path/to/folder
This merges the hidden ._ metadata files macOS creates on non-Apple filesystems back into their main files.
Corrupted ._ files are the single most common cause of -36 on flash drives that have been used on Windows machines too.
Run First Aid on the source and destination drives.

Open Disk Utility (Applications > Utilities).
Select each drive in the sidebar and click First Aid > Run.
If First Aid reports errors and can't repair them, the drive is failing — back up what you can and replace it.
Try copying via Terminal instead of Finder.

Open Terminal and run: cp -R ~/source/folder ~/destination/
Terminal's cp is much less strict than the Finder about metadata mismatches and will often complete a copy the Finder gave up on.
If cp also fails on the same file, the file or the drive is the issue — not the Finder.
Zip the folder before copying.

Right-click the source folder and choose Compress.
Copy the resulting .zip file — it's a single byte stream, so metadata problems inside the folder don't matter during the copy.
Unzip on the destination side.

When to Call a Professional

Error -36 is almost never something a technician fixes — it's a software or drive-health issue.
If Disk Utility's First Aid reports problems on the source drive, replace the drive before it gets worse.
If First Aid is clean and the same file keeps failing, the file itself is the issue — try a different copy method (Terminal cp, or zip the folder first).

Frequently Asked Questions

Why does the same file keep failing with -36 even after a restart?

If a specific file fails every time you copy it, the issue is the file itself or the sector of the drive it lives on.
A clean macOS restart doesn't change either of those.
Run Disk Utility First Aid on the source drive — if First Aid reports a repair, retry the copy.
If First Aid is clean but -36 still happens on that one file, try copying just that file with Terminal cp.
If cp also fails, the file's data on disk is genuinely unreadable and the file needs to be restored from a backup.