540EZ Profile issues with new 2015 firmware - revert back to old to make it work again.
I had to "dumb down" the firmware on the V6 to 2014 specs to get it to function again. Basically, the Cactus triggered the front red sensor (to be constantly on) and didn't fire the 540 while in TTL mode - only M. Learning failed also. Dumbing it back down to an older firmware fixed it (I knew it would work as the flash worked before I upgraded all the modules). If anyone is having similar issues with other flashes, try this fix.