Error codes.

error -50 paramErr: error in user parameter list

What format are these network drives & using SMB or AFP?

The error code -3403D simply means my computer won't run the internet-based AHT or the Command+D one because it's too old.

ME.sh

#!/bin/bash
Yellow="$(tput bold; tput setaf 226)"
White="$(tput bold; tput setaf 15)"
Normal="$(tput sgr0)"

MACERRORS="/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/CarbonCore.framework/Versions/A/Headers/MacErrors.h"

egrep -m1 "\-?$1" "$MACERRORS"
exit 0

Dependencies: current Xcode release.

Safe Boot from the HD, (holding Shift key down at startup), does the problem occur in Safe Mode?

What format are the other end?

As I recall things like too many files at root of FAT drives, illegal Chrs , etc.

Ok, would appreciate it, haven't seen a lot of -50 errors in the last decade or more, good luck. :)

Oh, did you disable AFP in File Sharing?

One strange cure her, try one...

https://discussions.apple.com/thread/3719997?answerId=18059661022#18059661022

You should post here IN THIS THREAD what you posted HERE > https://discussions.apple.com/thread/251030664

My network hard drives are SMB. My network originally consisted of one airport extreme with four airport express boosters. I had one airport express stop working, then my airport extreme stopped working. I purchased a Netgear AC1750 and two weeks afterwards the -50 error code started when I would transfer video files to the network hard drives. Does anyone have any ideas for solving my problem?

All of my network hard drives are formatted for mac OS X extended journaled. I have a 2007 mac pro that I have been using to transfer video files to the network drives. I have not encountered the -50 error code with it, just the iMac.

I tried your suggestion and the problem does occur in Safe Mode. Do you have any idea of what might be causing this?