I bought a Yongnuo YN560-II and it doesn't seem to want to accept my camera (6D). I have a pair of RF-603 triggers, which are also Yongnuos. I have one under my flash hot shoe and on on top of my camera's hot shoe. The triggers both light up and confirm connection, I can even fire my shutter using the trigger off camera. The flash is on, but won't fire. Is this a problem on my side or the camera not being compatible?