I'm not an electrician, but I do have a bit of experience with using Lutron 3-way dimmers with LED fixtures.
As someone else pointed out, you can use multiple dimmers if you are using the right dimmers, such as the Lutron Maestro. In that set up I believe there is a "master" switch and a "slave" or accessory switch. If that's the model you are using, and you have them installed correctly per Lutron's directions, that's not the problem.
While I do like them, I have found the Lutron digital switches to be very delicate. You will notice on the directions that they state to turn off all power when doing anything but changing a bulb. This is not only a safety issue for you, it is a safety issue for the switch. I have learned to turn off power even when changing a lightbulb for these switches. It seems the slightest thing can blow out the switch (I have lost at least one switch due to a power failure - there must have been a surge when the power was restored - only the Maestro switch was affected).
On some of these digital switches there is also a "reset" tab. You need to pull that out to set up the switch. See the instruction sheet for the exact procedure.
If you aren't using the Lutron Maestro switches, ignore the above. If you are, it is possible the above may apply.
