I have rioutil working perfectly with my fiancee's Rio S35S, but I couldn't get it to work with my new Rio Cali.
I found that usb-storage was claiming the Cali when it was plugged in. Sure enough, I can delete/write files to the Cali just by mounting it is a drive in Linux.
I would LIKE to use rioutil... Can I somehow block the usb-storage module from claiming the Cali?
I'm having the same issue, and apparently this is new. There is some discussion on it in the Help forum for rioutil. The name of the thread is " Missing file riofck?"