Files in Folders Won't Transfer from Hard Drive to Hard Drive (Error Code -50)

You might run Disk Utility's First Aid routine on the problematic drive(s). There may be some minor directory corruption that is giving the OS fits.

If your Mac can't save files to an external drive - Apple Support

Repair a storage device in Disk Utility on Mac - Apple Support

I just pulled this from the web via AI:

❝Error code -50 on a Mac is a common Finder error that typically occurs when you try to copy, move, or delete files. It usually indicates an "unexpected error" where the system cannot read or write data, often due to unsupported characters in a filename, disk corruption, or temporary system glitches. 

Quick Fixes

• Relaunch Finder: This is often the fastest fix. Click the Apple menu > Force Quit, select Finder, and click Relaunch.
• Rename the File: Check the file or folder for special characters (like :, /, or \) that might be causing conflicts. Try renaming it to something simple (e.g., "test"). ❞

You use these Ex-FAT formatted to exchange data with Windows PCs?

If not, then consider reformatting them with an Apple format; APFS or Mac OS Extended.