Quite a few theories have popped up about why certain USB sticks are failing. I suspect that there is no single reason why these USB sticks fail, but more that different types of USB sticks are failing for different reasons.

I'll jot down the main theories here, along with links to threads where they have been discussed.

One user reported having problems when his USB stick was formatted in Mac OSX. He then tried formatting it from Windows (7?) and it worked fine.

Other Mac users have reported that it works fine as long as you pick “FAT32” and the “MBR” option, which they said was the default for them (perhaps not for others?)

Justin Pope from the facebook group found that if you insert the troublesome USB prior to powering up, it works, but if you insert it after power up and go straight to BASIC, it doesn't. He suspects that some USB sticks take a longer time to register with the system.

Spannernick from the community forum reported that he had a troublesome USB stick that seemed to only work if you loaded a game from the carousel first (E.g., Alleykat or Avenger) and then jumped to basic. This seemed to not only trigger the fast-loader and D81 file support, but also got his troublesome stick to work!

• https://community.thec64.com/d/137-a-couple-of-questions

One user hinted at it in the referenced link above. I should check this out at some stage. If so, it might imply that users of Windows 10 will need to download some 3rd party formatting tool rather than relying on the one inside Windows 10.

Jumpmanjr suggested formatting the USB stick from the command-line:

1. Hit the Windows start button and type: CMD and hit ENTER.
2. Type the following command: format /FS:FAT32 /Q X: (Replace X with the drive letter of your USB-stick) and hit ENTER.