RF-603 not firing studio heads - two red lights

[the_local_jacko]

I have used RF-603's which i used with my Lencarta SmartFlashes for a few shoots and they worked flawlessly. The last few shoots however I can not seem to get them to fire the lights. I have put one in my D800 hot shoe and connected the other into the sync port of the SmartFlash. They both show two green lights then when I press the shutter the right hand LED on the RF-603 flashes red simultaneously on both units and doesn't fire the light. I've tried switching flash head, tried it using a D90, changed batteries etc with the same results. I have the camera in manual at 160th f8. When I use a sync cable instead the flash fires fine.

Any one had something similar?