client has 6 recessed cans with two three ways controlling them. He has the BR30 type fluorescent bulbs in each of the cans. The problem is when the switch is OFF the bulbs flicker.

Here is the items that i have checked in the device box. (No neutral available in the device box)
>Voltage to grounding with the lights ON 119V
>voltage to grounding with the lights OFF 23V
>The 23V disappears as soon as i connect a resistive load (obvious Phantom voltage)
>NO dimmer connected
> client has already replaced the switches with new ones.

The existing CFLs are about 1 year old so I asked the customer to change the bulbs with new CFLs and see if the flickering goes away.

What could be causing the flickering on the CFLs

I had that problem with a motion switch and a CFL.

Programmable switches or dimmers can cause this, due to a very small leakage voltage triggering a capacitor somewhere in the bulb. Any 'leakage', [say a track on switch insulation] can cause this too- it can be so small as to be unnoticed when using filament bulbs. Since it is a 'load' it will not trigger an RCD or GFCI. Some CFLs also glow dimly for a short while when turned off. IMHO, not worth worrying about.

Consider running a snubbing resistor in the circuit. Select a resistance high enough to do the job without drawing significant power... say 10kOhms.

If you really HAVE to.

Replace one of the bulbs with an incandescent.

Switches with the lighted handles can cause this as well.

Just a shot in the dark, but is this an old house where the hot and neutral wires might be reversed?

Thank you for your replies.

The switches are not lighted and the wiring to that part of the house is new.
one of my colleagues suggested a shared neutral with another circuit or a minor short between the ungrounded conductors with another circuit.

I will go back out on Thursday to troubleshoot.

I see this regularly on my ghetto houses. Usually I find voltage from neutral to ground. Other devices on that circuit might have the same problem. The pain in the butt ones get run a new neutral.

I've seen this problem with LED (GU10) lamps, but perhaps it could happen with CFLs too.
Found that capacitive coupling between the cores of (fairly long) switch runs, used for multi position switching, was the cause.
The fix was a small capacitor accross the first lamp in the chain. If I remember correctly a 0.1 microfarad, as used for interference suppression, did the trick. Obviously needs to be rated to be accross supply voltage.