It would seem that cryptic zone means slightly different things to some different people... Basically, in setting up a dark sump with live rock in it, I've had people call that a cryptic zone. Whether or not that's truly a cryptic zone, I'm not completely sure. The article linked above makes me wonder if it really fits the definition.
Can you describe more about what's not working so well for you?
What are you trying to have in your tank?
Can you list more details about your tank (equipment, lighting and such)?