I already used dfu-util
and this message has always been displayed but it doesn't affect the Reset. Once you execute
dfu-util -R -D u-boot-dfu.bin
you should get U-Boot console through serial port (ttyS0... or ttyUSB0 if you are using a Serial to USB dongle...) using minicom or a similar tool.
I ported U-Boot on the Hitex board in SPI Flash and using USB to get the console during a internship, so maybe I can help you further.