I had the same problem with my TriggerTrap at first. I figured out, it was a loose contact. Try to pull out the plug out the jack a little (0.5 mm or so) and try again. If it works then, you have two options. Either send the TriggerTrap back and wait for a replacement or (that's the way I went) open the casing and bend the contacts of the female jack - so the contacts of the plug fit.
I glued it together and had no problems again so far. It seems, the quality control of TT has some room for improvement.