USB booting :: Cannot find KNOPPIX file system

I tried lots of DSL embedded versions on my Kingston Data Traveler 2. When I qemu boot, it's fine but I keep getting Cannot Find KNOPPIX file system, sorry when actually booting. Some versions actually worked once or twice but now they won't work again. I'm using the same computer and same usb. Why is this happening?
Try the waitusb boot option to give time for USB to register.
I tried that and it still doesn't work.

original here.