Error Message: That name cannot be used for a spot color because it is reserved for the process plates.

Easy, don't use Cyan, Magenta, Yellow or Black as names for spot colors, because they are already in use as the default printing inks.

Can you recall the exact steps that led to this message? Were there any color duplicates as you set up your swatches? Were you trying to name or rename a swatch? If so, were you naming it in the panel (double clicking the name) or in the color dialog (presented when you double click the swatch itself)?

I recall receiving this message once, but I can't recall exactly what the actions were that triggered it. More important, I recall solving the problem. If you can describe your steps, it may job my memory.

What name are you trying to use when you get that message?