Please tell me why, when I enter the expression below, I get an error and dialog box which says Enter Parameter Value for today(). I have also tried Date() and Now().
DaysHeldDWT: IIf([Date_from_DWT] Is Null,[today()]-[Date_to_DWT],[Date_from_DWT]-[Date_to_DWT])
DaysHeldDWT: IIf([Date_from_DWT] Is Null,[today()]-[Date_to_DWT],[Date_from_DWT]-[Date_to_DWT])