I ran into that problem a couple days ago. I have four 1000H, two 700H and a 300H on protoboards mounted inside my fixture. Power comes from a Mean Well SP-200-48 and control from my Reef Angel, both mounted in my stand. There is a piece of lamp cord connecting the power supply to a pair of binding posts on the back of the fixture and a piece of Cat 5 plugs into the fixture to control the 4 channels. when I first set it up the white channel on one heat sink and the RB on the other heatsink would not dim. I did a lot of troubleshooting before I figured out that my conections at the data cable jack were the problem. If you get signal to the driver, it will dim. If it doesn't dim, find out why it's not getting the signal.
Of course, the following night I was cursing the LDD's for dimming all the way to zero. It seems that my white channel went down to 1 instead of zero and I had 20 LEDs that I could not shut off. You'd be surprised by how much light you get from 20 LEDs at 1%! Roberto at Reef Angel helped me out by supplying a few lines of code. It looks like it was a floating decimal point error when the unit had calculated the parabola for sunrise/sunset.
Everything works well now and I'm quite happy that I went with the LDD's. I really have to praise Reef Angel. They been great with their support, not only with the issue above, but also in setting me up with a 5v version of the PWM expansion module. There's a little more fine tuning to be done but I'm thrilled with how this project turned out.