Anyone have issues triggering a RF603N II with a D5100?

[SigmaPete]

Are there any known issues with using a Yongnuo RF603N II with a Nikon D5100? I am trying to trigger a Yongnuo 560 III with the RF603N II. When I mount the 560 III directly on the D5100, it triggers the flash from releasing the shutter. So it doesn't seem to be a problem with the hot shoe.

But when I have the RF603 mounted on the D5100 releasing the shutter will not trigger the 603 (and consequently the 560III) through the hotshoe. When I use the test button on the RF603 mounted on the D5100 it does trigger the flash remotely, so the 603 is clearly communicating with the 560III. For some reason it seems like my camera is not triggering the transmitting 603 through the hotshoe. Am I missing something here?

Any help is greatly appreciated. Thanks