BC30455 Error in Color coding

Hi

I have the following expression for color coding of SSRS cell. I dont know what is wrong here. Could one of you please help.

=IIF(

(Sum( IIf(Fields!Year_Key.Value = YEAR(TODAY),Fields!C_RA.Value,0) )  '2013
    -
Sum( IIf(Fields!Year_Key.Value = YEAR(TODAY)-1,Fields!C_RA.Value,0) ) '2012
)


 > 0, "Lime", "Red"

)

Error Code is BC30455.

Thanks