Fix 'The operation couldn’t be completed. (OSStatus error -36.)' on macOS

When does this error show up?

You're dragging a folder or file from your Mac onto an external drive—a USB stick, an SD card, or a portable hard drive formatted as FAT32 or exFAT. Halfway through, the copy stops. A dialog box says: 'The operation couldn’t be completed. (OSStatus error -36.)'

It happens most often with older drives or drives that were used on Windows machines too. I've seen it on macOS Ventura, Sonoma, and even the latest Sequoia beta. The file that fails is usually a small one—often a .DS_Store or a file with a weird character in the name.

What's actually causing error -36?

Error -36 is Apple's way of telling you that the file system on the destination drive can't handle something in the file's metadata. Specifically, it's a problem with the file's resource fork or extended attributes. Macs store extra info (like icon positions, Finder tags, or thumbnail data) in these hidden forks. When you copy to a non-Apple file system like FAT32 or exFAT, these forks have to be stripped or converted. If the drive has a corrupted directory entry or a filename with illegal characters (like a colon or a leading dot), the copy fails.

The real culprit is almost always a dot-underscore file (._filename) that's stuck on the external drive. These files are created by macOS to store resource forks on non-Apple drives. One gets orphaned or corrupted, and boom—error -36.

How to fix OSStatus error -36 (step by step)

The fix is simple: clean up those hidden dot-underscore files using the Terminal. You do not need to reformat the drive. Don't waste time with Disk Utility First Aid—it rarely helps here.

1. Connect the external drive to your Mac. Wait for it to show up in Finder. Note the drive's name exactly—spaces and all. For this guide, I'll use 'USBDRIVE' as the example.
2. Open the Terminal app. You'll find it in /Applications/Utilities/Terminal.app. Or just hit Cmd+Space and type 'Terminal'.
3. Change to the external drive's root directory. Type this and press Enter:
   

   cd /Volumes/USBDRIVE

   Replace 'USBDRIVE' with your drive's actual name. If the name has spaces, put quotes around it—like cd '/Volumes/My Drive'.
   Expected outcome: You should see no error. The prompt will just sit there, ready.
4. List all hidden dot-underscore files on the drive. Run this:
   

   ls -la ._*

   Expected outcome: You'll see a list of files starting with ._. If you see nothing, that's okay—the list might be empty. But usually you'll see a few dozen, especially if the drive has been used on multiple Macs.
5. Delete all those dot-underscore files. Run this command:
   

   dot_clean /Volumes/USBDRIVE

   This built-in macOS tool merges the resource forks back into the original files and then removes the orphaned ._ files. It's safer than a blanket rm ._* because it handles the merge properly.
   Expected outcome: The command runs and returns silently. No news is good news.
6. Verify the files are gone. Run ls -la ._* again. You should see nothing—or at least far fewer files. If you still see some, run dot_clean again with the -f flag (forces overwriting):
   

   dot_clean -f /Volumes/USBDRIVE

7. Try copying the file again. Go back to Finder and drag the folder or file that failed. It should copy now without the error. If it still fails, move to the next step.
8. Check for illegal filenames. Some file systems hate certain characters: colons (:), slashes (/), or names longer than 255 characters. Rename the file on your Mac so it uses only letters, numbers, hyphens, and underscores. Then copy again.

Still getting error -36? Try these last resorts

If the steps above didn't work, the drive might have deeper file system corruption. Here's what I'd check next:

• Run Disk Utility's First Aid on the external drive. Open Disk Utility, select the drive, click First Aid, then Run. It might find and fix directory errors that dot_clean can't touch.
• Copy files using the command line instead of Finder. Sometimes Finder's copy mechanism is more fragile. Use cp -R in Terminal:
  

  cp -R /path/to/source/file /Volumes/USBDRIVE/

  This bypasses Finder's metadata handling and might succeed where the GUI fails.
• Reformat the drive as exFAT (with a backup). If nothing else works, back up everything on the drive, then reformat it using Disk Utility. Choose 'exFAT' as the format—it works on both Mac and Windows and handles Mac metadata better than FAT32. After reformatting, restore your files. This will nuke the problem for good.

One more thing: if you're using an old USB 2.0 flash drive, consider replacing it. Cheap drives from five years ago have high failure rates. The error might be a hardware issue, not software. I've seen drives that produce error -36 reliably every few copies—they're dying. Toss them.

That's it. You should be copying files again in five minutes flat. Error -36 is annoying, but it's not a sign your Mac is broken. It's just a metadata headache, and now you've got the aspirin.