Have you configured your device yet?. This is the first time I’m using the USB flash drive Your USB flash drive might not be in the proper format. Plug it into your PC, open up “My computer,” right-click on the USB device, and select “Format.” Format the USB flash drive to FAT32. Make sure to save any files before doing this, as formatting will erase all data on the USB flash drive.
This is how to extract the files from an Xbox 360 ISO using a Mac. This will only really be useful if you have a JTAG. You will use a command line program called Extract xISO, as well as Terminal.
I’ve already configured it Try plugging in your USB flash drive after the console starts up and see if it appears. This is a very uncommon issue, but we’re aware of it and are working to correct the issue.
For now, just remember to plug in your USB flash drive after startup. If your USB flash drive suddenly has no data in it, or it has reverted to its pre-configured state, it may not meet all of the requirements for using it with the Xbox 360 console. If you got a warning message during configuration, find a USB flash drive that better meets the requirements for use with the console. If you want to give your USB flash drive another try, format it to FAT32 again on the PC and then try the configuration process again. Make sure to save your files on the console as well, in case you still encounter a problem.