It is possible that a SBC66 Boards board is not programmed with the Netcruzer USB Bootloader, or it got deleted.

Some early boards (prior to June 2012) were shipped without the Netcruzer USB Bootloader.
If programming a board with a PIC Programmer, the Netcruzer USB Bootloader will most likely get deleted.

To test if the Netcruzer USB Bootloader is present, place the jumper in the "F" position (Details), and reset the board. The LED should now flash as described here.

A PIC Programmer is required to restore the Netcruzer USB Bootloader, by programming the board with the correct hex file. The compiled version of the Netcruzer USB Bootloader is a hex file, and the name will indicate the target board it is meant for. For example, the "sbc66ec_bootloader.hex" file is for the SBC66EC board. These hex file can be obtained:

On the web at netcruzer.com/nz/firmware.php
In the ".../bin" folder of the Netcruzer Download

After obtaining the correct hex file, program the target board as described here.

The full source code is available, and located in the ".../src/projects/usb_hid_boot" folder of the Netcruzer Download.