It is a "known problem" with the X16, confirmed this with x-blue a couple of years ago. I thought they had licked that problem though.

Maybe you have an older KSU???

Call Ernie Meadows from X-blue to see if they can advance you a newer KSU.

I believe that the problem exists on Verizon lines based on the Central Office equipment used in your area. In other words, it may work with Verizon at certain Central Offices.
The predominant carrier where I am is Cablevision, so I have not seen this problem recently.

Bottom line is if you hook up a caller id unit and all works, it is an x-blue problem, not a carrier problem.

Walter