I have some Cactus V2S equipment that I am in the process of selling and encountered a problem(?) that I don't understand. A fellow came by to purcahse them and had Lumadyne studio strobes with portable power packs which the V2s wouldn't fire. We tried them on two different strobes with no luck. We then tried firing his strobes with my 40D and had no problem. Additionally I used the V2s to fire my 580 EX II and had no problem doing that. (?) Anyone have an explanation.