1) Did you format the drive to FAT32 with MBR (master boot record)?
2) When you downloaded the ZIP, did you use Safari? If so, it may have become corrupted; please use a different browser.
3) Did you unzip the firmware file from within the ZIP?
4) Did you place the update file on the root of the USB drive (not within a folder)?
5) Was that the only update file on the drive?
6) Does the controller boot into firmware update mode when you hold the Deck 2 RELOOP/EXIT and USB 1 STOP buttons as in the instructions?
7) Is the USB to the computer disconnected at the time?