Revised formula for the conditional formatting:
=AND(MOD(COLUMN(),2)=0,C1="y",D1="n")

Regards
Rowan

ForSale wrote:
Every column between C and AA will have either "y" or "n" in it. One
the odd columns starting with C, I need no conditional formatting. In
the even columns starting with D, I need a conditional format that will
turn the cell red if the cell to the left is "y" and this one is "n".
For example:
C D E F
y y n n
y n y y
n n y n

I need to be alerted to D3 and F4.

Thanks.