Here is additional information
Lightroom version: 5.6 
License type: Perpetual
Operating system: Windows 7 Ultimate Edition
Version: 6.1 
Application architecture: x64
System architecture: x64
Logical processor count: 8
Processor speed: 2.6 GHz
built-in memory: 12279.1 MB
Real memory available to Lightroom: 12279.1 MB
Real memory used by Lightroom: 328.6 MB (2.6%)
Virtual memory used by Lightroom: 303.6 MB
Memory cache size: 252.3 MB
Maximum thread count used by Camera Raw: 4
System DPI setting: 96 DPI
Desktop composition enabled: Yes
Displays: 1) 1920x1080
Application folder: C:\Program Files\Adobe\Adobe Photoshop Lightroom 5.6
Library Path: C:\Users\Andy\Pictures\Lightroom\Lightroom 5 Catalog-2.lrcat
Settings Folder: C:\Users\Andy\AppData\Roaming\Adobe\Lightroom
2) Canon Tether Plugin
5) jf PicasaWeb
6) Leica Tether Plugin
7) Nikon Tether Plugin
9) ProShow Web
- Config.lua flags: None
Adapter #1: Vendor : 10de
Device : 6e4
Subsystem : 83211043
Revision : a1
Video Memory : 487
AudioDeviceName: Speakers (Realtek High Definition Audio)
Renderer: NVIDIA GeForce 8400 GS
I am having the exact same problem. Would definitely like a solution.
I ended up talking to someone who is more familiar with LR on laptops and explained that I would be much better off to not try to copy my whole catalog from my desktop to my high end laptop. What we worked out is to just use the laptop catalog as I take pictures while I am on the road. Then we walked through exporting the catalog of only the pictures that I just imported from the camera. Small catalogs seem to export just fine…
Sent from Windows Mail
I think the real problem is with the USB HDD, For hard drives to run efficiently there needs to be lots of available room on the drive. If a drive is over 75% full it will not function efficiently. To copy 36GB of info a drive needs a lot more than that space available to complete the copy process. So if the drive is a 1TB drive with only 100Gb free you will have problems. (the 100GB of free space may be scattered in small pockets over the entire drive.) To wit a 160Gb drive with 100Gb free will be more efficient that a 1Tb drive with 100Gb free.
Solution found. I shut down the CC Cloud connection and this worked fine. BTW, my catalog is about 18k pictures. It took about 3 hours to export to the USB drive, but successful. In my case, my cat and files are primarily on my desktop, however when I travel I want access to them on my LT, plus this provides a backup copy of all of my pictures.
Thanks for commenting…In my case I tried it on two separate USB drives both with over 100GB free for my 36GB catalog of pictures. Since I changed tactics I will not try this again but someone else commented that they solved a similar problem they had by shutting down their connection to their cloud drive. While I am not using a cloud drive for this operation I recall I did have problems when my Android phone was plugged in so I can see where it could make sense that a cloud drive would somehow interfere with a disk based operation. Adobe should make these kinds of issues better known because they are frustrating.
That makes sense…I recall I had problems with disk based operations when my android phone was plugged into my PC at the same time I was doing things in LR even though I was not using LR to access the memory cards in the phone. Apparently LR does not like USB drives unless it has exclusive access to them and is not somehow confused by cloud drives or android based devices. Thanks for your thoughts.