Lighting, Light Fixtures, Ceiling and Exhaust Fans - Install Electronic Low Voltage Dimmer

Help Please!!! I am baffled. I installed Hampton Bay Low Voltage Track lighting and am trying to install a low voltage dimmer. I bought the one they said I needed at Home Depot. It is Commercial Electric #202-743. I am installing this in a 3 way application. My problem is that there are 5 wires on the dimmer., and only 4 wires in the box. I have installed other switches and dimmers but am pretty much a novice.

According to the instructions for 3-way installation it tells me to 1. connect the green wire to the ground (OK) (Copper wire)
2. Connect the Red wire to the wire that had been connected to the different colored screw on the original switch (OK) (Black)
3. Connect the Black wire to either one of the wires removed from the existing switch (OK) (Red)
4. Connect the Yellow wire to the other wire removed from the existing switch
(White)
5. Connect the White wire to the neutral----This is where I am baffled!! I only have 4 wires---If the white is neutral, it is already connected to the Yellow wire. :(

Can anyone help me???? As far as I know the wiring is standard--Where does the 5th wire get connected?? Please help.

Thanks

You have a switch that requires a neutral, and no neutral in the box. This switch cannot be used in this location. Are there no other wires in the box than these four. Not even something tucked way into the back of the box?