“File or Document” Can’t Be Opened Because The Original Item Can’t Be Found

Good afternoon MadMax889,

Welcome to the Apple Support Communities!

We'd like to help with the issue you are having transferring files between your MacBook Pro and Mac mini to one or more external drives.

We recommend updating your computers to the most recent operating system for the models that you have.

For best results, external drives should be formatted Mac OS Extended (Journaled) and attached directly to the computer. Files can then be copied and moved via Finder with ease.

The resources below will help you with this:

Erase and reformat a storage device in Disk Utility on Mac - Disk Utility User Guide

Connect and use other storage devices with Mac - macOS User Guide

Take care.

OK - that helps. I didn't see that you were trying to copy between the two drive on the Mac mini.

Ultimately, mounting both drives and copying via the MacBook Pro is going to be the least efficient way, especially given the permissions issue you're seeing.

Instead I'd take a different approach - the easiest would be to enable screen sharing on the MacMini - then you can simple connect to the Mini from the MacBook Pro and see the full desktop, moving files between the drives as if you were on the machine itself.

Share the screen of another Mac - Apple Support

Other options that come to mind hinge around the same idea... logging onto the machine (via something like SSH) and moving the files via command line, or using Remote Apple Events to move the files, but both are more complex than just sharing the screen over the network.

It isn't quite clear what your situation is, which may may diagnosis/troubleshooting/solutions harder.

From what I've weaned so far, you have two machines - A MacBook Pro and a Mac mini.

The MacMini is attached to your TV, right?

The MacMini has an external drive (or drives) attached, right?

You're trying to mount those external drives over the network on your MacBook Pro, right?

When it comes to moving files, are you trying to move files to/from the MacBook Pro? or move them between the internal and external volumes on the Mac Mini? I can't quite wean that from the information provided, but I'm having trouble seeing where the 'original item can't be found' message is coming from.