That's the correct cable. I would check the following:
- You're using Dynamic C 9.62 or earlier. Dynamic C 10 is for newer products (based on Rabbit 4000, 5000 and 6000).
- You have selected the correct serial port. You can verify by seeing the selected port disappear from port lists when you unplug the cable.
- The BL2100 has power.
- You're using the "PROG" and not "DIAG" connector on the programming cable.
- The red edge of the ribbon cable matches the pin 1 marking of the programming connector (silkscreen dot, typically the edge of the board).
Hope that helps.