Hey there, I was trying to figure out how to use a Yonguo-YN560 as a slave using a Cowboy Studio NPT-04 wireless flash trigger setup, with a Canon 580EXII as the master in E-TTL mode(on a Canon 60D). I know the Yongnuo has to be in either S1 or S2 mode for slave use. When I set it to S1 mode, I saw that it fired noticeably earlier than the shutter release, which I later found out is due to the 580EXII firing off multiple flashes while in E-TTL mode. I tried it in S2 mode, which is apparently supposed to ignore the first flash and only fire on the second, but I get absolutely nothing, the Yongnuo doesn't even fire at all. Let me also note that if I have the Yongnuo in M or S1 mode, when I fire the pilot on my wireless trigger, the Yongnuo fires, but in S2 mode I get nothing from the trigger's pilot. If I try the Yongnuo's on-camera pilot button, it pops fine. I have fresh batteries in everything, so I know that isn't the problem.