If you have tried everything else, and are still getting errors like "not in sync", read this.
The older version of the FTDI board had proper through-hole soldered pins. The 6 pin header socket on the latest verison is surface mounted!! This is a terrible design, and a poor way to save a few cents. The 2nd or 3rd time I plugged it in, it wouldn’t talk to the Arduino. I closely examined it, and found the track had been broken on the 1st and 2nd solder pads.
This is no surprise, as it is a mechanical component, soldered to pads at the end of hair-width traces on the board, and has no mechanical structural support. It only took a slight lift as I handled it to break 2 tracks. I am not a clumsy person, and was very disappointed to see it was destroyed in about 2 hours.
All it needed was to be glued to the board and this would have been avoided, or remain with the through-hole pins. It is very poor design. I have no way to repair such a small circuit trace. I have managed to get it to work, but it is very ugly and will not last long.
@Sparkfun - Please revise your motives for making the header socket SMD. It is poor design.