I created a boolean parameter called graphic in crstal reports version 8.0

and I am using it as a suppression formula for some border options of a text object. when I put the following formula in for suppressing the line style it works fine but when I try to use the same formula for the drop shadow I get an error 'The formula result must be boolean'. the formula is
IF {?graphics}=True THEN 0

Why would this formula work for some supression option but not for others ?

Thanks For Your Help !
Stephen J. Hunt