I’m pretty sure deponia is wrong - what’s the purpose of having a flash drive if you can’t back your files up?
I’m running Win7 64bit and have created both backups and repair disks on a SanDisk Extreme usb 3.0 and on an Ultra USB 3.0 - no issues! what I did do is format it to exFAT as my disk image was kinda huge (around 15GB) so it couldn’t be stored in FAT32.
Most operating systems ask for removable drives for backup and image file creation so just make sure that your drive shows up as removable and is formatted to either exFAT or NTFS and you should be good to go. If you buy a large drive (64gb and above) it should be formatted to exFAT already.
If not check if your drive’s working fine otherwise.