Unable to upload Amiga Roms - Failed to get files for package

I’ve only had the developer licence for the XBox One for a couple of days. I followed a very good tutorial on how to get RetroArch onto the XBox using the XBox Portal from my PC. That worked perfectly, I can see and run RetroArch on the XBox and have updated all of the cores, etc.

I renamed my Amiga ROMs as per instructions and then came to upload them to the XBox, this is where everything has ground to a halt.

The instructions I have are to use the XBox Portal in my browser to access File Explorer. And then to upload the kickstart ROMs to LocalAppData/RetroArch/LoadState/system.

I can get as far as being able to click on the link to expand the RetroArch folder, but it just eventually times out with the error

Javascript from “xxx.xxx.xxx.xxx” Failed to get files for package 1e4cf179-f3c2-404f-b9f3-c62070a5aad8_1.10.3.0_x64_8ngdn9a6dx7ma

I tried resetting my PC and XBox in case they needed it, but nothing.

My second attempt after reading through various websites was to download My Files Explorer onto the XBox via the Portal from my PC. This transferred fine and could be run from the XBox. I have a portable hard drive I keep movies and music on to play through the XBox, so I transferred the kickstart ROMs onto that and plugged it into the XBox.

The XBox detected the drive and allowed me to select it for Media. I can see it in Settings/System/Storage Devices, but when I ask it to “view contents” it briefly displays the Windows Store icon, then a blank store page background (no icons, text, heading, nothing).

I tried My Files Explorer but all that show me is This Device Media Servers Archer Router Isolated Storage

It will not show me my USB Drives

I even ran RetroArch and tried to use the File Browser on there, but again the USB Drive is never displayed (it is formatted to NTFS and is USB 3.0 for reference).

I am at a complete loss as to what to do next.

Can anyone help?