transferring songs from one external hd to another external hd

[kenpattx]

This is a very elementary problem that I have, but I'm no computer geek.
I have performed this process previously with no problems. I have a MTU Laptop, added my songs to an external HD (USB) because the one in the laptop was too small to accommodate them. I copied that external HD(I called "F") to another external HD (called "G",")for "insurance" purposes, and carried that HD with us in case we needed it. It is a back up HD only. I added a number of new cdgs to my primary external HD ("F") over the past few months, but did not add them to the secondary HD("G"). In the past, all I did was format my backup HD, and copied F to G. This weekend, I decided to perform this task so that both HD's were identical, but ran into problems. It seemed to go well until the last 30 minutes of copying, and then I got a message "unable to copy CB20058-8, file path is too deep". It stops there and after 3 tries, I decided to call for someone's brains to help.The problem isn't that there isn't enough space on the HD...I checked that and there is plenty of space for it. I have never seen that message before. Please walk me through exactly what I need to do to accomplish this task. for purposes of helping me, pretend that I know nothing (not far from the truth) and go step by step.
I also have a MTU Shuttle computer, which I also need to do this task on, but am afraid to touch it. It is a back up computer...In case I do something stupid to my laptop.....
Thank you in advance for your help. Pat

"You can do anything that you wanna do, but you can't take away my MTU"