I have been using my 6D with Excalibur flash unit for months, and suddenly it has stopped working with my camera. I can't figure out what is wrong. The flash is firing if I press the test button on the flash cord, but it's no longer speaking to my camera, so doesn't fire when I press the shutter. I wouldn't be surprised at all if it's something strange I've done with my settings, although I haven't touched them much lately. I feel like i must have done something! The camera otherwise is working fine. Can anyone shed light on this (pun intended)? I am new to using flash at all, so please bear with me!