I'm sorry to tell you that, with USB sticks, it's a matter of trial and error to find one that'll work. For example, I plugged in about 5 sticks I had laying about until I found one that worked (a 2GB Micro Cruzer).
Can you try using an SD card? I've not yet found an SD card that won't work with the CCK (I use a 16GB one). I either use it on it's own or I have a USB stick style card reader should I need to use that to access the card via a computer (and it doesn't have a card drive).
Marilyn